Cationic electrodeposition coating and application thereof

ABSTRACT

The present invention relates to
         a cationic electrodeposition coating composition, which provides an uncured electrodeposited film having storage elasticity modulus (G′) at 140° C. within a range of from 80 to 500 dyn/cm 2  and loss elasticity modulus (G″) at 80° C. within a range of from 10 to 150 dyn/cm 2 , and which is superior in smoothness and edge coatability; and   a method for establishing both of smoothness and edge coatability therewith; as well as;   a cationic electrodeposition coating composition comprising crosslinked resin particles having an average particle size within a range of from 1.0 to 3.0 μm and thermal softening temperature within a range of from 120 to 180° C.; and   a method for producing a cationic electrodeposition film having established smoothness and edge coatability, wherein the cationic electrodeposition film is prepared by applying a voltage to an article immersed in a cationic electrodeposition coating composition, and wherein the cationic electrodeposition coating composition comprises crosslinked resin particles having an average particle size within a range of from 1.0 to 3.0 μm and thermal softening temperature within a range of from 120 to 180° C.       

     The present invention can provide a method for establishing both of surface smoothness and edge coatability of the cationic electrodeposition coating composition, and cationic electrodeposition coating composition which can provide an electrodeposition film having excellent surface conditions.

TECHNICAL FIELD

The present invention relates to a cationic electrodeposition coatingcomposition superior in smoothness and edge coatability and a method forsatisfying both of the smoothness and the edge coatability of a cationicelectrodeposition film using the same.

Further, the present invention relates to a cationic electrodepositioncoating composition superior in smoothness and edge coatability,specifically a cationic electrodeposition coating composition superiorin smoothness and edge coatability which comprises a specificcrosslinked resin particle, and a method for satisfying both of thesmoothness and edge coatability of a cationic electrodeposition filmusing the same.

BACKGROUND OF THE INVENTION

Electrodeposition coating is a coating process carried out by immersingan article to be coated in an electrodeposition coating composition andapplying a voltage. Since the electrodeposition coating process canautomatically and continuously coat an article to be coated having acomplicate shape to a nicety, it has been widely and practically used asa process for primarily coating a large size article having complicateshape such as, in particular, an automobile body.

Since the electrodeposition coating is a coating on an article, it isnaturally desirable that coated surface is smooth. Further, theperforation portion of metal and the like have sharp edge and unless acoated film is adequately coated on the edge portion, anticorrosiveperformance is deteriorated. Consequently, both of surface smoothnessand edge coatability are performances required for the electrodepositioncoating. On the other hand, the surface smoothness is obtained bylowering the viscosity of the uncured coating film at curing by bakingto be fluidized, but the edge coatability is obtained by keeping so asnot lowering the viscosity of the uncured coating film. Namely, the edgecoatability requires the suppression of sagging of coating film atcuring the coating film and the coating film remains also at sharp edge.Namely, the surface smoothness and the edge coatability are conflictingperformances.

Technology relating to the coating film viscosity of theelectrodeposition film is described in Japanese Patent ApplicationPublication No. 2002-285077 (Patent document 1) and it describes anelectrodeposition coating composition for an electric wire wherein theminimum coating film viscosity at the curing process of coating film isbetween 30 to 150 PaS (claim 3). The patent document 1 describes edgecoatability and the like can be improved without sagging at melt byadjusting the minimum coating film viscosity at the curing process ofcoating film.

Japanese Patent Application Publication No. 6-65791 (Patent document 2)discloses a process for coating an anti-chipping primer on an uncuredcoating film surface formed by coating a cationic electrodepositioncoating composition, further carrying out an intermediate coating and atop coating, and curing the three layers simultaneously, wherein theminimum melt viscosity during curing the coating film of the cationicelectrodeposition coating composition is 10⁴ to 10⁸ cps. It disclosesthat since the three layers of the coating films are baked only at once,coating steps are shortened, it is superior in edge covering propertyand the resulting coating film consisting of a plurality of layers issuperior in finishing property and anti-chipping property. Thepublication discloses the finishing property and edge covering propertyin the coating film consisting of a plurality of layers, but does notstudy the finishing property and the edge covering property on anelectrodeposition film itself. On the other hand, it has beenconventionally carried out in general coating compositions including thecationic electrodeposition coating composition of the present inventionthat the viscosity of the coating film is controlled using a particledescribed later.

By the way, the reduction of ash contents in the electrodepositioncoating composition has been recently promoted. The reduction of ashcontents is that the amount of solid components with a high specificgravity such as an inorganic pigment is reduced and that sedimentationis designed not to occur in the solid contents of the electrodepositioncoating composition. The reduction of ash contents reduces energy andlabor for stirring an electrodeposition bath hitherto for prevention ofsedimentation. Accordingly, when the content of an inorganic pigment isreduced in order to correspond the request of the above-mentionedreduction of ash contents, the quantity of resin contents in the coatingcomposition is relatively enhanced, the viscosity of the uncured coatingfilm obtained by the electrodeposition coating cannot be appropriatelyincreased, and as a result, the control of sagging at an edge portioncannot be suitably adjusted to the lower edge coatability.

On the other hand, since solid concentration of about 20% by weight isused in the current cationic electrodeposition coating composition,rinsing with water is carried out at several steps separately after theelectrodeposition coating, and a baking step is carried out aftercompletely removing the electrodeposition coating composition adhered onthe article unnecessarily, in particular, its solid contents.Accordingly, a large quantity of rinsing water is used, the rinsing stepwith water is elongated and the reduction of rinsing water and theshortening of the rinsing steps with water has been recently desired. Asthe means for shortening the rinsing step with water, the furtherlowering of solid concentration in the coating composition of 20% byweight, so-called low solid content is required. However, when such lowsolid content is simply carried out, the sedimentation of solid contentsin the electrodeposition coating composition occurs easily because ofthe lowering of the coating composition viscosity, and the like. Whenthe content of an inorganic pigment is further reduced as describedabove, the sedimentation of solid contents occur further easily.Consequently, the stirring in an electrodeposition bath must be carriedout in order to prevent the sedimentation, and the reduction of energyload is difficult. Namely, a cationic electrodeposition coatingcomposition capable of controlling viscoelasticity so as to easily carryout the edge coatability, and superior in surface smoothness and preventthe sedimentation, has been desired, even if low solid content isrealized for energy saving and the shortening of steps.

In relation to a means for obtaining such coating composition, namely acoating composition improved in thixotropy, there exist severaltechnologies adding crosslinked resin particles to the cationicelectrodeposition coating composition. Japanese Patent ApplicationPublication No. 2005-23232 (Patent document 3) discloses that minuteresin particles with a particle size of 0.01 to 0.2 μm whose inside wascrosslinked are added to a cationic electrodeposition coatingcomposition (Patent document 3, claim 6). It has been conventionallyexisted as improving thixotropy that resin particles with such smallsizes are added in the electrodeposition coating composition.

Japanese Patent Application Publication No. 2002-212488 (Patent document4) discloses a cationic electrodeposition coating composition thatcomprises crosslinked resin particles obtained by carrying out theemulsion polymerization of α,β-ethylenically unsaturated monomer mixtureusing an acryl resin having an ammonium group as an emulsifier, in orderto improve the anticorrosive property of an edge portion of an article.The resin particles obtained herein is small with a particle size of0.05 to 0.3 μm. However, when a crosslinked resin particles with anaverage particle size of 1.0 μm or less are added in anelectrodeposition coating composition, the smoothness of the resultingcoating film is lowered.

Patent document 1: Japanese Patent Application Publication No.2002-285077Patent document 2: Japanese Patent Application Publication No. 6-65791Patent document 3: Japanese Patent Application Publication No.2005-23232Patent document 4: Japanese Patent Application Publication No.2002-212488

SUMMARY OF THE INVENTION Disclosure of the Invention Problem to beSolved by the Invention

It is the object of the present invention to provide a method forsatisfying both of the conflicting performances of the surfacesmoothness and edge coatability in a cationic electrodeposition coatingcomposition, as described above.

Further, it is the object of the present invention to provide a methodfor lowering the solid concentration in a cationic electrodepositioncoating composition, preventing the sedimentation of the coatingcomposition for reduction of ash contents, and satisfying both of theconflicting performances of the surface smoothness and edge coatabilityin a cationic electrodeposition coating composition, as described above.

Means for Solving Problem

Accordingly, the present invention provides a cationic electrodepositioncoating composition, which provides an uncured electrodeposited filmhaving storage elasticity modulus (G′) at 140° C. within a range of from80 to 500 dyn/cm² and loss elasticity modulus (G″) at 80° C. within arange of from 10 to 150 dyn/cm², and which is superior in smoothness andedge coatability.

The cationic electrodeposition coating composition preferably comprisesa cationic epoxy resin, a blocked isocyanate curing agent, and ifnecessary, a resin particle (preferably a crosslinked resin particle)and/or a pigment (preferably an inorganic pigment).

The present invention further provides a method for producing a cationicelectrodeposition film having established smoothness and edgecoatability, wherein the cationic electrodeposition film is prepared byapplying a voltage to an article immersed in a cationicelectrodeposition coating composition, which includes steps of:

adjusting storage elasticity modulus of an uncured electrodeposited filmof the cationic electrodeposition coating composition (G′) at 140° C.within a range of from 80 to 500 dyn/cm², and

adjusting loss elasticity modulus of an uncured electrodeposited film ofthe cationic electrodeposition coating composition (G″) at 80° C. withina range of from 10 to 150 dyn/cm².

In order to adjust storage elasticity modulus and loss elasticitymodulus, addition of a crosslinked resin particle or an inorganicpigment is preferable. The crosslinked resin particles preferably havean average particle size within a range of from 1.0 to 3.0 μm. Thecontent of the crosslinked resin particles is preferably 3 to 15% byweight relative to weight of resin solid contents in the cationicelectrodeposition coating composition.

The inorganic pigment is added to the cationic electrodeposition coatingcomposition, wherein content of the inorganic pigment is preferably 10to 20% by weight relative to weight of solid contents in the cationicelectrodeposition coating composition, in order to adjust storageelasticity modulus and loss elasticity modulus.

In order to adjust storage elasticity modulus and loss elasticitymodulus, both of an inorganic pigment and crosslinked resin particleshaving an average particle size within a range of from preferably 1.0 to3.0 μl can be added to the cationic electrodeposition coatingcomposition, wherein content of the inorganic pigment is preferably 0.5to 10% by weight relative to weight of solid contents in the cationicelectrodeposition coating composition,

In the case that both of an inorganic pigment and crosslinked resinparticles are added to the cationic electrodeposition coatingcomposition in order to adjust storage elasticity modulus and losselasticity modulus, it is preferable that the content of the crosslinkedresin particles is 3 to 15% by weight relative to weight of resin solidcontents in the cationic electrodeposition coating composition.

The present inventors have investigated a method for establishing bothof surface smoothness and edge coatability in a cationicelectrodeposition coating composition with low solid and low ashcontent. The present inventors found that addition of a certaincrosslinked resin particle to a cationic electrodeposition coatingcomposition easily and facilely could solve the problem and reached tothe present invention.

Accordingly, the present invention provides a cationic electrodepositioncoating composition comprising crosslinked resin particles having anaverage particle size within a range of from 1.0 to 3.0 μm and thermalsoftening temperature within a range of from 120 to 180° C., which issuperior in smoothness and edge coatability.

The content of the crosslinked resin particles is preferably 3 to 15% byweight relative to weight of resin solid contents in the cationicelectrodeposition coating composition.

The present cationic electrodeposition coating composition is preferablya cationic electrodeposition coating composition with low solid and lowash content comprising no inorganic pigment or a inorganic pigment nomore than 7% by weight relative to weight of the solid contents in thecationic electrodeposition coating composition.

The present cationic electrodeposition coating composition has a solidconcentration within a range of from preferably 0.5 to 9% by weight.

In the present invention, the crosslinked resin particles may beprepared from (a) a compound preferably having two or more unsaturateddouble bonds in the molecule and (b) a (meth)acrylate by a known methodsuch as a suspension polymerization, emulsion polymerization, etc.

The present invention further provides an uncured electrodeposited filmof a cationic electrodeposition coating composition, which has storageelasticity modulus (G′) at 140° C. within a range of from 80 to 500dyn/cm² and loss elasticity modulus (G″) at 80° C. within a range offrom 10 to 150 dyn/cm².

The present invention further provides a cured cationicelectrodeposition film having no more than 0.25 μm of Ra value (as anindex of smoothness of a coating film), which is obtained by curing thecationic electrodeposition coating composition.

The present invention further provides a method for producing a cationicelectrodeposition film having established smoothness and edgecoatability, wherein the cationic electrodeposition film is prepared byapplying a voltage to an article immersed in a cationicelectrodeposition coating composition, and wherein the cationicelectrodeposition coating composition comprises crosslinked resinparticles having an average particle size within a range of from 1.0 to3.0 μm and thermal softening temperature within a range of from 120 to180° C.

The present invention further provides a method for producing a cationicelectrodeposition film having improved smoothness and edge coatabilityfrom a cationic electrodeposition coating composition with low ash andlow solid content, which includes steps of:

adjusting storage elasticity modulus of an uncured electrodeposited film(G′) at 140° C. within a range of from 80 to 500 dyn/cm², and

adjusting loss elasticity modulus of an uncured electrodeposited film(G″) at 80° C. within a range of from 10 to 150 dyn/cm²,

wherein the cationic electrodeposition coating composition comprisescrosslinked resin particles having an average particle size within arange of from 1.0 to 3.0 μM and thermal softening temperature within arange of from 120 to 180° C. and content of the crosslinked resinparticles is 3 to 15% by weight relative to weight of resin solidcontents in the cationic electrodeposition coating composition.

EFFECT OF THE INVENTION

According to the present invention, both of the smoothness and edgecoatability can be established by simultaneously adjusting losselasticity modulus G″ and storage elasticity modulus G′ among thedynamic viscoelasticities of an uncured electrodeposited coating filmduring the electrodeposition coating. In a conventional technology,smoothness has been secured only by managing the lowest melt viscosityby controlling complex viscosity coefficient η* in the measurement ofdynamic viscoelasticity, but it was grasped that the compatibility ofthe above-mentioned smoothness and the edge coatability was impossibleby only viscosity merely. In the present invention, it has been foundthat it is important to control loss elasticity modulus: G″ (viscosityitem) within a specified range at controlling the smoothness, in dynamicviscoelasticities of an uncured coating film of a cationicelectrodeposition coating composition.

Further, it has been found that it is important to control the storageelasticity modulus G′ (elastic item) in a specified range at controllingthe edge coatability. Further, in the present invention, it has beenfound that it is important to control the loss elasticity modulus G″ ina specific range and to simultaneously control the storage elasticitymodulus G′ in a specific range in order to secure the both of thesmoothness and edge coatability of the electrodeposition film, that hasbeen conventionally considered as a contradictable event. The both ofthe established smoothness and the edge coatability of the resultingelectrodeposition film have been achieved by considering these G″ and G′as independent parameters and controlling these parameters withinrespective specific ranges.

According to the present invention, both of the established surfacesmoothness and edge coatability can be evaluated only by controllingboth of the loss elasticity modulus and storage elasticity modulus of anuncured electrodeposited film by an electrodeposition coating. A methodfor performance test or performance management useful for a cationicelectrodeposition coating composition can be provided.

Further, according to the present invention, both of the establishedsurface smoothness and edge coatability are possible by addingcrosslinked resin particles with an average particle size within a rangeof from 1.0 to 3.0 μm and thermal softening temperature within a rangeof from 120 to 180° C. to a cationic electrodeposition coatingcomposition. Since increase of the viscosity in a coating film cannot beachieved by an inorganic pigment in case of a low ash type cationicelectrodeposition coating composition, it is anticipated that the edgecoatability is deteriorated, but the edge coatability is also improvedby adding the specific crosslinked resin particles to the cationicelectrodeposition coating composition according to the present inventionand it is effective as a means for keeping or improving the coating filmperformance in the low ash type cationic electrodeposition coatingcomposition. Herein, the low ash type cationic electrodeposition coatingcomposition means that an inorganic pigment is not contained at all inthe solid contents in the cationic electrodeposition coating compositionor even if it is contained, it is up to 7% by weight relative to theweight of the solid contents in the composition (i.e., a cationicelectrodeposition coating composition with low ash content). Further, inthe present invention, there is provided the low solid type cationicelectrodeposition coating composition that is superior in an ability ofpreventing sedimentation than the conventional one and enables theestablishment of the surface smoothness and the edge coatability asdescribed above. Herein, the low solid type cationic electrodepositioncoating composition means that the solid content concentration of thecationic electrodeposition coating composition is lower than theconventional 20% by weight, and within a range of from specifically 0.5to 9% by weight (i.e., a cationic electrodeposition coating compositionwith low solid content).

In the study by the present inventors, the establishment of both of thesurface smoothness and edge coatability can be correlated withmeasurement of dynamic viscoelasticities of the resultingelectrodeposited film by the electrodeposition coating. In particular,when the loss elasticity modulus G″ at 80° C. and the storage elasticitymodulus G′ at 140° C. are within specific ranges, namely, the losselasticity modulus G″ at 80° C. is 10 to 150 dyn/cm², and the storageelasticity modulus G′ at 140° C. is 80 to 500 dyn/cm², both of thesurface smoothness and the edge coatability are established, but in thepresent invention, it has been found, as an solving means, thatcrosslinked resin particles with an average particle size within a rangeof from 1.0 to 3.0 μm and thermal softening temperature of 120° C. ormore are added to the cationic electrodeposition coating composition.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph showing the behaviors of the loss elasticity modulus(G″) values in the dynamic viscoelasticities in five coatingcompositions.

FIG. 2 is a graph showing the behaviors of the storage elasticitymodulus (G′) values in the dynamic viscoelasticities in five coatingcompositions.

FIG. 3 is a graph showing the behaviors of the complex viscositycoefficient (η*) values in the dynamic viscoelasticities in five coatingcompositions.

FIG. 4A is a graph showing a relation between the storage elasticitymodulus (G′) at 80° C. and electrodeposition texture in several coatingcompositions.

FIG. 4B is a graph showing a relation between the complex viscositycoefficient (η*) at 80° C. and electrodeposition texture in severalcoating compositions.

FIG. 4C is a graph showing a relation between the loss elasticitymodulus (G″) at 80° C. and electrodeposition texture in several coatingcompositions.

FIG. 5A is a graph showing a relation between the storage elasticitymodulus (G′) at 140° C. and electrodeposition texture in several coatingcompositions.

FIG. 5B is a graph showing a relation between the complex viscositycoefficient (η*) at 140° C. and electrodeposition texture in severalcoating compositions.

FIG. 5C is a graph showing a relation between the loss elasticitymodulus (G″) at 140° C. and electrodeposition texture in several coatingcompositions.

FIG. 6A is a graph showing a relation between the storage elasticitymodulus (G′) at 80° C. and edge coatability in several coatingcompositions.

FIG. 6B is a graph showing a relation between the complex viscositycoefficient (η*) at 80° C. and edge coatability in several coatingcompositions.

FIG. 6C is a graph showing a relation between the loss elasticitymodulus (G″) at 80° C. and edge coatability in several coatingcompositions.

FIG. 7A is a graph showing a relation between the storage elasticitymodulus (G′) at 140° C. and edge coatability in several coatingcompositions.

FIG. 7B is a graph showing a relation between the complex viscositycoefficient (η*) at 140° C. and edge coatability in several coatingcompositions.

FIG. 7C is a graph showing a relation between the loss elasticitymodulus (G″) at 140° C. and edge coatability in several coatingcompositions.

FIG. 8 is a graph showing a relation between temperature and storageelasticity modulus G′ for illustrating the thermal softeningtemperature.

FIG. 9 is a view schematically showing a part in a distance of 30microns from an edge of a cutter knife blade.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The dynamic viscoelasticity is an elasticity modulus observed whenvibrational (periodical) strain or force (stress) is applied to a linearviscoelastic body, and depends on a vibrational number and temperature.The description related to the dynamic viscoelasticity below refers tocontents described in Rheology (edited by Japan Rheology Academy), thesecond section: Polymer liquid rheology, pages 31 to 39; and PolymerChemistry, Introduction (edited by Seizo Okamura, Akio Nakajima,Shigeharu Onogi, Yasunori Nishijima, Toshinobu Higashimura and NorioIse), the fourth section: Various performances of polymer substances,Viscoelasticities, pages 149 to 155.

Stress and strain at an angular velocity [ω(2π×frequency F)] areprovided by the following formulae.

Strain γ(t)=γ₀ e ^(iωt)(dyn/cm²)

Stress σ(t)=σ₀ e ^(i(ωt+δ))(dyn/cm²)

wherein γ(t) is a strain at a time (t), σ(t) is a stress at a time (t),γ₀ is a strain at t=0, σ₀ is a stress at t=0, and δ represents phasecontrast.

The complex elasticity modulus G* is represented by the equation:

G*=(σ₀/γ₀)e ^(iδ)=(σ₀/γ₀)(cos δ−i sin δ)

The complex viscosity coefficient [η*=G*/ω(poise)] generally used as aviscosity control factor of a coating composition is obtained byquantifying viscoelasticity having properties in combination of both ofviscosity and elasticity of the coating composition.

Namely, in the present invention, viscosity and elasticity are graspedseparately, and the establishment of both of the smoothness and edgecoatability was enabled by controlling them respectively. It isnecessary for securing smoothness to control the flowability of thecoating composition at the baking process. Viscous properties arerelated to the flowability, and this is represented by the followingformula according to a relation between stress and strain.

Loss elasticity modulus (viscosity) G″=G* sinδ(dyn/cm²)

On the other hand, it is necessary for the securing the edge coatabilityto control a force going to remain at the site at the baking process,and the force is related with elastic properties. This is represented bythe following formula according to a relation between stress and strain.

Storage elasticity modulus (elasticity) G′=G* cos δ(dyn/cm²)

In case of a general coating composition including a cationicelectrodeposition coating composition, the viscosity item dominates anuncured coating film at the initial stage of a baking process, and thecomposition is greatly subjected to an influence of the loss elasticitymodulus G″. At the posterior stage, the uncured coating film is reachedto a gelation point (apparently, in a continuous state in both ends) bya fusing and a pseudo-crosslinking. The elastic item dominatesthereafter, and the film is greatly subjected to an influence of thestorage elasticity modulus G′. The gelation point is a temperature atwhich a relation between the loss elasticity modulus G″ (the viscosityitem) and the storage elasticity modulus G′ (the elastic item) asviscoelasticity-behaviors during the baking process is (Loss elasticitymodulus G″)<(Storage elasticity modulus G′). Namely, it means a point atwhich the domination by the viscosity item is changed to a domination bythe elastic item.

In the present invention, it has been found that the establishment ofboth of the smoothness and edge coatability is enabled by the control ofthe loss elasticity modulus G″ at temperature (80° C.) no more than thegelation point and the control of the storage elasticity modulus G′ attemperature (140° C.) no less than the gelation point, and the presentinvention was achieved thereby.

Herein, the present invention is described by an explanation of theprocess by which the present invention has been achieved. Firstly, thefollowings were carried out as preliminary experiments.

Viscoelastic behaviors were observed for several coating compositions,specifically, a conventional coating composition to which componentssuch as a pigment were added, a coating composition without them, and acoating composition comprising a crosslinked resin particle. Theviscosity of the coating compositions begins to be lowered at 40 to 80°C. in accordance with the rising of the temperature, the viscosity isslightly raised between about 80 and about 100° C., and when it exceeds100° C., the viscosity is greatly decreased to be flown. After theflowing, the curing reaction starts to raise the viscosity again, toraise it gradually till nearby 150° C. and then, the viscosity isabruptly raised to complete the curing. In order to investigate thedynamic viscoelasticities of the coating composition while confirmingit, five coating compositions were measured using Rheosol-G3000 by UBMCorporation, and strain values γ(t) for stress values ρ(t) applied andphase contrast δ between stress and strain were measured underconditions of a strain of 0.5 degree, a frequency of 0.02 Hz and atemperature rising rate of 2° C./min. The storage elasticity modulus(G′), the loss elasticity modulus (G″) and the complex viscositycoefficient (η*) are calculated according to the above formulae from therelations between the resulting stress values σ(t), strain values γ(t)and phase contrast δ, and are respectively shown in FIG. 1 to FIG. 3.The coating compositions used in FIGS. 1 to 3 are as followings: “STD”is PN-310 (a cationic electrodeposition coating composition:manufactured by Nippon Paint Co., Ltd.); “Pigment free” is a coatingcomposition without any pigment components in the PN-310 (PWC=0%);“Resin particle 1” is a coating composition in which 15% by weight ofcrosslinked resin particles (with average particle size of 1 to 3 μm)were added to the “Pigment free”; “Resin particle 2” is a coatingcomposition in which 5% by weight of crosslinked resin particles (withaverage particle size of 100 nm) were added to the “Pigment free”; and“Resin particle 3” is a coating composition in which 10% by weight ofcrosslinked resin particles (with average particle size of 100 nm) wereadded to the “Pigment free”, which particles are different from those inthe “Resin particle 2”.

As seen from FIGS. 1 to 3, it is grasped that the behaviors areconsiderably different depending on the respective coating compositions.Almostly, it is divided into 3 modes (40 to 80° C., 80 to 100° C. and100° C. or more), but it can be grasped that the behaviors of thedynamic viscoelasticities are greatly changed depending on theformulations of the coating compositions, in particular, in the presenceof the components such as the particles, and that these graphs depictedby five coating compositions are different. Accordingly, it is alsograsped that the behaviors of the dynamic viscoelasticities can beoptimally controlled by changing the formulation.

In particular, viewing FIGS. 1 to 3, it can be understood that greatdifferences between respective coating compositions are based on thebehavior of the viscoelasticity nearby 80° C. and the behavior of theviscoelasticity nearby 140° C.

Further, the following experiments were carried out based on thesebases. Several coating compositions, such as PN-310 (a cationicelectrodeposition coating composition: manufactured by Nippon Paint Co.,Ltd.); a coating composition in which the amount of the inorganicpigment component in the PN-310 coating composition was changed; acoating composition in which an inorganic pigment component was removedfrom the PN-310; and a coating compositions in which the kind and amountof the crosslinked resin particles to be added in the last compositionwere changed, were prepared, and viscosity behavior for each of them wasmeasured. From the results of their viscoelasticities, threeviscoelasticity behaviors at 80° C., namely, all of G′ values andelectrodeposition texture (FIG. 4A), η* values and electrodepositiontexture (FIG. 4B) and G″ values and electrodeposition texture (FIG. 4C)were displayed in FIG. 4 so that changes at the respective temperaturesare easily grasped from the result of those viscoelasticities.Similarly, three viscoelasticity behaviors at 140° C., namely, all of G′values and electrodeposition texture (FIG. 5A), values andelectrodeposition texture (FIG. 5B) and G″ values and electrodepositiontexture (FIG. 5C) were displayed in FIG. 5. Further, theelectrodeposition texture is represented by a surface roughness (Ra).The electrodeposition texture evaluated herein means the appearance ofelectrodeposition film described later, namely smoothness, and thatrepresented by the measurement value of the arithmetic average roughness(Ra) of a roughness carve. Namely, the relation between theelectrodeposition texture and the viscoelasticity behavior is observedby evaluating the above-mentioned smoothness by the electrodepositiontexture.

As seen from the behaviors of FIGS. 4 and 5, there is a correlation withthe electrodeposition texture at 80° C. in the relation between theviscoelasticity change and electrodeposition texture at the respectivemeasurement points and in the measured coating compositions (see FIG.4C). Further, similarly, the measuring results of the behaviors of theedge coatabilities and three viscoelasticity behaviors are described inFIGS. 6A to 6C and FIGS. 7A to 7C. As seen from FIGS. 6 and 7, it isgrasped that the relation between the storage elasticity modulus (G′) at140° C. and the edge coatability exhibits a correlation (see FIG. 7A).Namely, it means that the change of the viscosity value and theelectrodeposition texture (smoothness) or the edge coatability have acorrelation. Herein, the above-mentioned edge coatability can bedetermined by an evaluation method described later. Further, the“coatability” represented in FIGS. 6 and 7 is the same meaning as the“edge coatability” mentioned here.

From these measuring results, it is found that, as an evaluation basis,the present invention can employ the loss elasticity modulus (G″) at 80°C. for the electrodeposition texture (smoothness) and the storageelasticity modulus (G′) at 140° C. for the edge coatability. The presentinvention has been completed thereby. Further, the preferable ranges ofthe storage elasticity modulus (G′) and the loss elasticity modulus (G″)can be selected referring to the appended FIGS. 4 and 7. Namely, G′ at140° C. is within a range of from preferably 80 to 500 dyn/cm² referringto FIG. 7A, and G″ at 80° C. can be selected within a range of from 10to 150 dyn/cm² referring to FIG. 4C (the smaller electrodepositiontexture Ra means the better smoothness). The storage elasticity modulus(G′) is within a range of from preferably 90 to 500 dyn/cm² and morepreferably from 100 to 500 dyn/cm². Further, the loss elasticity modulus(G″) at 80° C. is within a range of from preferably 10 to 120 dyn/cm²and more preferably from 10 to 100 dyn/cm².

When the storage elasticity modulus (G′) is lowered than the desirablelower limit of the storage elasticity modulus (G′), there is a fear thatthe edge coatability of the electrodeposition film obtained isdeteriorated, and when the storage elasticity modulus (G′) exceeds thedesirable upper limit, there is a fear that smoothness is lowered. Whenthe loss elasticity modulus G″ is lowered than the desirable lower limitof the loss elasticity modulus G″, there is a fear that although thesmoothness is improved, the edge coatability of the electrodepositionfilm obtained is deteriorated, and when the loss elasticity modulus G″exceeds a desirable upper limit, there is a fear that smoothness islowered.

Herein, the storage elasticity modulus G′ and the loss elasticitymodulus G″ are relate to the elasticity modulus of uncuredelectrodeposited film. The “uncured” means a state in which anelectrodeposited coating film obtained by carrying an electrodepositioncoating of a cationic electrodeposition coating composition is not curedyet by baking.

The cationic electrodeposition coating composition, as described above,contains or comprises a crosslinked resin particle and/or an inorganicpigment, but further contains an aqueous medium; a binder resincontaining a cationic epoxy resin and a blocked isocyanate curing agentdispersed or dissolved in an aqueous medium; a neutralizing acid; and anorganic solvent.

In order to adjust the above-mentioned viscoelasticity behaviors, thereis a process of adding a crosslinked resin particle, as a first process.The average particle size of the crosslinked resin particles is within arange of from preferably 1.0 to 3.0 μm. When the average particle sizeis smaller than 1.0 μm, the proportion of the surface area is increased,and interaction with a cationic epoxy resin or the like, as binder resincomponents, contained in the cationic electrodeposition coatingcomposition is increased, and the viscosity of the deposited coatingfilm is abruptly raised; therefore the above-mentioned adjustments ofviscoelasticity behaviors become difficult. On the other hand, when theparticle size is larger than 3.0 μm, the lowering of smoothness causedby the sedimentation of the electrodeposition coating composition at nostirring and by the accumulation of particles applied on a horizontalplane upon coating occurs.

Further, the crosslinked resin particles used in the present inventionhave preferably an average particle size within a range of from 1.0 to3.0 μm and a thermal softening temperature of 120° C. or more and withina range of from preferably 120 to 180° C. for establishing both of thesurface smoothness and the edge coatability of a cationicelectrodeposition coating composition with low ash and low solidcontent. Although a proposal of an addition of crosslinked resinparticles in cationic electrodeposition coating composition is carriedout also in a. conventional technology, the resin particles are almostthose having an average particle size of less than 1.0 μm. Since resinparticles are added for merely controlling the viscosity in aconventional technology, the resin particles with an average particlesize of less than 1.0 μm are required, but in the present invention, thecrosslinked resin particles having a larger average particle size thanthat in the conventional technology and a thermal softening temperatureof 120° C. or more and within a range of from preferably 120 to 180° C.are preferably added for the achievement of establishing both of thesurface smoothness and the edge coatability, from the view point of thedynamic viscoelasticities, in particular, from the view points of theloss elasticity modulus (G″) at 80° C. and the storage elasticitymodulus (G′) at 140° C.

The average particle size of the crosslinked resin particles used in thepresent invention is within a range of from 1.0 to 3.0 μm, as describedabove, but the lower limit is preferably 1.2 μm and further preferably1.5 μm. On the other hand, the upper limit is preferably 2.5 μm andfurther preferably 2.2 μm. As described above, when it is less than 1.0μm, it is within the range of the average particle size of resinparticles in a conventional technology, and it is not preferable becausethe surface smoothness is deteriorated. The crosslinked resin particleshaving an average particle size of more than 3.0 μm provide the loweringof smoothness caused by the sedimentation in an electrodepositioncoating composition at no stirring and by the accumulation of particleson a horizontal plane at an electrodeposition coating caused bydropping. The average particle size herein can be measured by the methodbelow.

The average particle size of the resin particles is measured by agranular particle transmission measurement method using MICROTRAC9340UPAmanufactured by Nikkiso Co., Ltd. Further, the particle sizedistribution of the resin particles is measured in a measurement device,and the average particle size at cumulative relative frequency F(x)=0 iscalculated from the measurement values. These measurements andcalculations employ the refractive index of 1.33 of solvent (water) andthe refractive index of 1.59 of the resin content.

The crosslinked resin particle used for the present invention have athermal softening temperature within a range of from 120 to 180° C., asdescribed above, for establishing both of the surface smoothness and theedge coatability in a cationic electrodeposition coating compositionwith low ash and low solid content, but the upper limit value ispreferably 140° C. and more preferably 160° C.

When the thermal softening temperature is lower than 120° C., thestorage elasticity modulus G′ is not a given value at baking the uncuredelectrodeposition film, and the edge coatability cannot be secured. Onthe other hand, a material in which the thermal softening temperature ofthe crosslinked resin particle exceeds 180° C. cannot substantially besynthesized.

The thermal softening temperature is a temperature at which thecrosslinked resin particle starts to be softened. Namely, G′ values atthe respective temperatures of the objective crosslinked resin particlesare determined. The temperature at a point at which the changes of G′values for the temperature changes are abruptly changed is called as athermal softening temperature. It can be determined according to thefollowings. The storage elasticity modulus G′ of a sample obtained byadjusting the concentration of the crosslinked resin particles to 30% byweight (as a solid content) is measured from 90° C. under conditions ofa strain of 0.5 degree, a frequency of 0.02 Hz and a rising temperaturerate of 4.0° C./min in a temperature dependent measurement withRheosol-G3000 (manufactured by UBM Corporation) that is a rotationaltype dynamic viscoelasticity measurement device. The measurement resultsare shown in a graph in FIG. 8. As seen in FIG. 8, although the storageelasticity modulus G′ of the crosslinked resin particle keeps a constantviscosity at an initial temperature region (about 90 to 140° C. in FIG.8), the lowering of the storage elasticity modulus G′ begins to occur ata temperature (temperature exceeding 140° C. in FIG. 8). The tangentialline in an area at which viscosity is a constant and the tangential linein an area at which the lowering of viscosity occurs are drawn, and thetemperature at the cross point is defined as a thermal softeningtemperature.

In order to increase the thermal softening temperature of the resinparticle, the crosslinking degree of the resin particle is required tobe increased. It is necessary for securing the thermal softeningtemperature area in the present invention that the resin particle is acrosslinked resin particle. Glass transition temperature is also anindex of softening of a resin, but when the glass transition temperature(Tg) is measured in the crosslinked resin particle, it reaches at alevel of several hundred order (° C.); therefore the thermaldecomposition of the resin is frequent at the temperature, and thesoftening property of particle itself cannot be observed. Accordingly,the thermal softening temperature is employed in the present invention.

Further, the crosslinked resin particle is required to have acrosslinking structure. In case of no crosslinking structure, the valueof the above-mentioned storage elasticity modulus G′ at 140° C. is lessthan 80 dyn/cm², and it is not preferable because the edge coatabilitycannot be secured. The crosslinked resin particle is preferably used inan amount of 3 to 15% by weight relative to the weight of the solidresin contents of the cationic electrodeposition coating composition.When the content of the crosslinked resin particles is less than 3% byweight, the establishment of both of the surface smoothness and the edgecoatability is difficult, and when it exceeds 15% by weight, there is afear that the lowering of a coating film performance such asanticorrosion property is provided. Herein, the “solid resin content(s)”mean(s) all of the solid content(s) weight of the resin components(including the crosslinked resin particles) contained in the cationicelectrodeposition coating composition.

The content of the crosslinked resin particles in the present inventionis within a range of from preferably 3 to 15% by weight relative to theweight of the solid resin contents in the cationic electrodepositioncoating composition with low ash and low solid content for establishmentof both of the surface smoothness and the edge coatability, but itslower limit is preferably 4% by weight and further preferably 5% byweight. On the other hand, its upper limit is preferably 10% by weightand further preferably 8% by weight.

Considering that the average particle size of the crosslinked resinparticles is within a range of from 1.0 to 3.0 μm, they are preferablyproduced by a suspension polymerization. Although it is also possible toproduce them by other process such as an emulsion polymerization iftheir particle size and the thermal softening temperature satisfy theabove-mentioned range, but the suspension polymerization is preferablefrom the aspect of arranging the particle size within a desired range.

The crosslinked resin particles include, but are not specificallylimited to, for example, resin particles containing a resin having acrosslinking structure obtained by mainly using an ethylenicallyunsaturated monomer, resin particles containing a urethane resininternally crosslinked, fine resin particles containing a melamine resininternally crosslinked, and the like.

The above-mentioned resin having a crosslinking structure obtained bymainly using an ethylenically unsaturated monomer includes, but is notspecifically limited to, for example, resin particles internallycrosslinked that are obtained by carrying out a suspensionpolymerization of a monomer composition containing a crosslinkingmonomer as an essential component and an ethylenically unsaturatedmonomer, in an aqueous medium, to prepare an aqueous dispersion, andsubstituting the above-mentioned aqueous dispersion with a solvent;resin particles internally crosslinked obtained by a NAD method ofdispersing resin particles internally crosslinked that are obtained bycarrying out the copolymerization of a monomer composition containing acrosslinking monomer as an essential component and an ethylenicallyunsaturated monomer, in a non-aqueous organic solvent that dissolves amonomer but does not dissolve a polymer such as a low SP organic solventsuch as an aliphatic hydrocarbon, a high SP organic solvent such as anester, a ketone and an alcohol, or by a sedimentation-precipitationmethod, or the like.

The above-mentioned ethylenically unsaturated monomer includes, but isnot specifically limited to, for example, the alkyl esters of acrylicacid or methacrylic acid such as methyl (meth)acrylate, ethyl(meth)acrylate, n-butyl(meth)acrylate, isobutyl (meth)acrylate and2-ethylhexyl (meth)acrylate; styrene, α-methylstyrene, vinyl toluene,t-butylstyrene, ethylene, propylene, vinyl acetate, vinyl propionate,acrylonitrile, methacrylonitrile, dimethylaminoethyl (meth)acrylate, andthe like. Two or more of the above-mentioned ethylenically unsaturatedmonomers may be used in combination.

The above-mentioned crosslinking monomer includes, but is notspecifically limited to, for example, a monomer having 2 or more ofethylenically unsaturated bonds, that are radically polymerizable, inthe molecule, a monomer having 2 or more of ethylenically unsaturatedgroups respectively supporting mutually reactive groups, etc.

The monomer having 2 or more of ethylenically unsaturated bonds, thatare radically polymerizable, in the molecule, that can be used for theproduction of the above-mentioned internally crosslinked fine resinparticles includes, but is not specifically limited to, for example, thepolymerizable unsaturated monocarboxylic acid esters of polyalcoholssuch as ethylene glycol diacrylate, ethylene glycol dimethacrylate,triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate,1,3-butylene glycol dimethacrylate, trimethylolpropane triacrylate,trimethylolpropane trimethacrylate, 1,4-butanediol diacrylate, neopentylglycol diacrylate, neopentyl glycol dimethacrylate, 1,6-hexanedioldiacrylate, pentaerythritol diacrylate, pentaerythritol triacrylate,pentaerythritol tetraacrylate, pentaerythritol dimethacrylate,pentaerythritol trimethacrylate, pentaerythritol tetramethacrylate,glycerol dimethacrylate, glycerol diacrylate, glycerolaryloxydimethacrylate, 1,1,1-trishydroxymethylethane diacrylate,1,1,1-trishydroxymethylethane triacrylate, 1,1,1-trishydroxymethylethanedimethacrylate, 1,1,1-trishydroxymethylethane trimethacrylate,1,1,1-trishydroxymethylpropane diacrylate and1,1,1-trishydroxymethylpropane dimethacrylate; polymerizable unsaturatedalcohol esters of polybasic acids such as triallyl cyanurate, triallylisocyanurate, triallyl trimellitate, diallyl terephthalate and diallylphthalate; aromatic compounds substituted with 2 or more of vinyl groupssuch as divinyl benzene, etc.

The combination of mutually reactive functional groups existing in theabove-mentioned monomer having 2 or more of ethylenically unsaturatedgroups respectively supporting mutually reactive groups includes, but isnot specifically limited to, for example, the combinations of an epoxygroup and a carboxyl group, an amino group and a carbonyl group, anepoxy group and a carboxylic anhydride group, an amino group and acarboxylic acid chloride group, an alkyleneimino group and a carbonylgroup, an organoalkoxysilane group and a carboxyl group, a hydroxylgroup and isocyanate glycidyl acrylate group, and the like. Amongothers, the combination of an epoxy group and a carboxyl, group is morepreferable.

The above-mentioned resin particles containing a urethane resininternally crosslinked are fine resin particles composed of polyurethanepolymer that is obtained by reacting a polyisocyanate component with anactive hydrogen containing component having diol having a hydroxy groupat a terminal and diol or triol having a carboxyl group to form apolyurethane prepolymer containing an isocyanate terminal group having acarboxylic acid salt at a side chain, and successively reacting theprepolymer with a chain elongating agent containing an active hydrogen.

The polyisocyanate component used for the above-mentioned prepolymerincludes aromatic diisocyanates such asdiphenylmethane-4,4′-diisocyanate, tolylene diisocyanate and xylylenediisocyanate; aliphatic diisocyanates such as hexamethylene diisocyanateand 2,2,4-trimethylhexane diisocyanate; alicyclic diisocyanates such as1-cyclohexane diisocyanate,1-isocyanato-3-isocyanatomethyl-3,5-trimethylcyclohexane (isophoronediisocyanate), 4,4′-dicyclohexylmethane diisocyanate andmethylcyclohexylene diisocyanate; and the like. The above-mentionedpolyisocyanate component is more preferably hexamethylene diisocyanateand isophorone diisocyanate.

The above-mentioned diol having a hydroxy group at a terminal includes,but is not specifically limited to, for example, polyether diol,polyester diol or polycarbonate diol having a molecular weight of 100 to5000 and the like. The diol having a hydroxy group at a terminalincludes, but is not specifically limited to, for example, polyethyleneglycol, polypropylene glycol, polytetramethylene glycol, polybutyreneadipate, polyhexamethylene adipate, polyneopentyl adipate,polycaprolactone diol, poly-3-methylvalerolactone diol,polyhexamethylene carbonate, and the like.

The above-mentioned diol containing a carboxyl group includes, but isnot specifically limited to, for example, dimethylol acetate, dimethylolpropionate, dimethylol lactate, and the like. Among others, dimethylolpropionate is preferable.

The above-mentioned triol includes, but is not specifically limited to,for example, trimethylol propane, trimethylol ethane, glycerinepolycaprolactone triol, and the like. The inside of urethane resinparticles has a crosslinking structure by using a triol.

The above-mentioned fine resin particles containing a melamine resininternally crosslinked include, but is not specifically limited to, forexample, melamine resin particles internally crosslinked that areobtained by dispersing a melamine resin and a polyol, in the presence ofan emulsifier, in water, and then, carrying out the crosslinkingreaction of the melamine resin and the polyol in the particles formed bydispersing; and the like.

The above-mentioned melamine resin includes, but is not specificallylimited to, for example, di-; tri-, tetra-, penta- and hexa-methylolmelamines and alkyl ethers thereof (alkyl is methyl, ethyl, propyl,isopropyl, butyl or isobutyl), and the like. As the above-mentionedmelamine resin that is commercially available, for example, resins suchas CYMEL 303, CYMEL 325, CYMEL 1156 (manufactured by Mitsui CytecIndustries Inc.) can be mentioned.

The above-mentioned polyol includes, but is not specifically limited to,for example, triol or tetrol having a molecular weight of 500 to 3000,and the like. The above-mentioned polyol is more preferablypolypropylene ether triol and polyethylene ether triol.

The above-mentioned crosslinked resin particles may be those obtained byisolating the internally crosslinked fine resin particles by methodssuch as filtration, spray drying and freeze drying, and pulverizing themto an appropriate particle size, as they are or using a mill, to be usedin a state of powder; an aqueous dispersion obtained as they are; orthose in which medium is replaced with solvent replacement to be used.

As the second process adjusting the above-mentioned viscoelasticitybehaviors, there is a process by which an inorganic pigment is used atan amount within a range of from 10 to 20% by weight (hereinafter,occasionally called as “PWC”) relative to the weight of the solidcontents of a cationic electrodeposition coating composition. In aconventional cationic electrodeposition coating composition, theabove-mentioned PWC exceeds 20% by weight, and is set as 25% by weightor less; therefore both of the smoothness and edge coatability could notbe established, but both of the smoothness and edge coatability can beestablished by using the PWC within a range of from 10 to 20% by weight.Herein, the PWC means a proportion for all of the solid contents of theresin components and pigment components contained in the cationicelectrodeposition coating composition. When the PWC of the inorganicpigment is less than 10% by weight, the content of a resin is much, andthe resin is softened by the rising of temperature; therefore objectivehigh viscosity cannot be obtained, and the above-mentioned viscositybehaviors cannot be adjusted. On the other hand, when the PWC exceeds20% by weight, pigments become adversely much, fusing effects by theresin cannot be obtained, and as a result, high viscosity is notexpressed; therefore the control of viscoelasticity is difficult.Further, as described above, the PWC for the inorganic pigment affectsthe viscosity behaviors, but the particle size does not affect theviscosity behaviors so much.

The inorganic pigment, as used herein, is not specifically limited sofar as it is a pigment usually used for an electrodeposition coatingcomposition. The example of the pigment includes inorganic pigmentsusually used, for example, coloring pigments such as titanium white andcolcothar; filler pigments such as kaolin, talc, aluminum silicate,calcium carbonate, mica and clay; anticorrosive pigments such as zincphosphate, iron phosphate, aluminum phosphate, calcium phosphate, zincphosphite, zinc cyanide, zinc oxide, aluminum tripolyphosphate, zincmolybdate, aluminum molybdate, calcium molybdate, aluminumphosphomolybdate, aluminum zinc phosphomolybdate, bismuth compounds andcerium compounds, etc.

The third process adjusting the above-mentioned viscoelasticitybehaviors is a process of using the above-mentioned crosslinked resinparticle and inorganic pigment in a combination. In this case, theaverage particle size of the above-mentioned crosslinked resin particlesis within a range of from 1.0 to 3.0 μm, and its amount to be used iswithin a range of from 3 to 15% by weight relative to the weight of thesolid contents in a coating composition. On the other hand, the amountof inorganic pigment to be used (PWC) can be reduced to within a rangeof from 0.5 to 10% by weight relative to the weight of the solidcontents in the cationic electrodeposition coating composition. Itslower limit is preferably 1% by weight, and further preferably 2% byweight. On the other hand, its upper limit is preferably 7% by weight,and further preferably 5% by weight. When it is used in an amountexceeding 10% by weight, the pigment amount is much more than thenecessary amount, and there is a fear of the deterioration of the planarappearance caused by the sedimentation of the pigment. Further, when itis less than 0.5% by weight, there is a fear of lowering color-hidingproperty.

The amount of the inorganic pigments can be further reduced by usingboth of the inorganic pigment and the crosslinked resin particle, and asa result, the reduction of energy and labor for preventing thesedimentation of the solid contents in the electrodeposition coatingcomposition can be expected. Further, when the viscoelasticity behaviorsare adjusted only by using the crosslinked resin particle without usingthe inorganic pigment, the above-mentioned energy and labor forpreventing the above-mentioned sedimentation of the solid contents canbe greatly reduced. Further, when the inorganic pigment is not containedor when an extremely small amount of the inorganic pigment is containedeven if the inorganic pigment is contained, the water rinsing step isgreatly shortened although the rinsing of a coated article with water iscarried out after the electrodeposition coating; therefore great effectsfor the simplification of the facilities and the reduction of usingresources are provided.

Then, components used for a general cationic electrodeposition coatingcomposition are described.

Cationic Electrodeposition Coating Composition

The cationic electrodeposition coating composition comprises an aqueousmedia; a binder resin comprising a cationic epoxy resin dispersed ordissolved in an aqueous media and a blocked isocyanate curing agent; aneutralizing acid; and an organic solvent. The cationicelectrodeposition coating composition may further comprise an inorganicpigment. Content of the inorganic pigment is preferably no more than 7%by weight relative to weight of the solid contents of the cationicelectrodeposition coating composition. As stated above, in order torealize the low ash content, the composition may comprise no inorganicpigments. As stated above, in the present invention, in order to providea low ash and/or low solid type cationic electrodeposition coatingcomposition having both of the surface smoothness and edge cotability,the cationic electrodeposition coating composition may comprise theparticular crosslinked resin particles.

Cationic Epoxy Resin

The cationic epoxy resin which may be employed in the present inventionincludes an epoxy resin modified with an amine. The cationic epoxy resinis typically produced by opening all of the epoxy rings of a bisphenoltype epoxy resin with an active hydrogen compound which can introduce acationic group, or by opening a portion of epoxy rings with other activehydrogen compound and then opening the residual epoxy rings with anactive hydrogen compound which can introduce a cationic group.

A typical example of the bisphenol type epoxy resin includes a bisphenolA type epoxy resin and a bisphenol F type epoxy resin. The commerciallyavailable product of the former includes YD-7011R (manufactured by TohtoKasei Co., Ltd., epoxy equivalent: 460 to 490), Epikote 828(manufactured by Yuka-Shell Epoxy Co., Ltd., epoxy equivalent: 180 to190), Epikote 1001 (the same manufacturer, epoxy equivalent: 450 to500), Epikote 1010 (the same manufacturer, epoxy equivalent: 3000 to4000) and the like, and the commercially available product of the latterincludes Epikote 807 (the same manufacturer, epoxy equivalent: 170) andthe like.

An oxazolidone ring-containing epoxy resin which is represented by thefollowing formula and disclosed in JP-A-5-306327:

wherein R means a residual group formed by removing a glycidyloxy groupof a diglycidylepoxy compound, R′ means a residual group formed byremoving an isocyanate group of a diisocyanate compound, and n means apositive integer, may be used as the cationic epoxy resin. This isbecause the resulting coating film is superior in heat resistance andcorrosion resistance.

An example of the method for introducing an oxazolidone ring into anepoxy resin includes reacting a polyepoxide with a blocked isocyanatecuring agent which has been blocked with a lower alcohol such asmethanol, in the presence of a basic catalyst, with heating and keepingits temperature, and distilling off a lower alcohol as a resultingby-product from the system to give the product.

It is known that a reaction of a bifunctional epoxy resin with amonoalcohol-blocked diisocyanate (i.e., bisurethane) gives anoxazolidone ring-containing epoxy resin. Examples of the oxazolidonering-containing epoxy resin and preparation thereof are known anddisclosed in JP-A-2000-128959, paragraphs 0012 to 0047.

Such epoxy resin may be modified with an appropriate resin such aspolyester polyol, polyether polyol and monofunctional alkylphenol.Furthermore, the epoxy resin can extend its chain by utilizing thereaction of an epoxy group with a diol or a dicarboxylic acid.

It is desirable that the ring of the epoxy resin is opened with anactive hydrogen compound so that an amine equivalent is 0.3 to 4.0meq/g, after ring opening, and the primary amino group occupies morepreferably 5 to 50% therein.

The active hydrogen compound which can introduce a cationic groupincludes the acid salts of primary amine, secondary amine and tertiaryamine, sulfide and an acid mixture. The acid salts of primary amine,secondary amine or/and tertiary amine(s) are used as the active hydrogencompound which can introduce a cationic group in order to prepare anepoxy resin containing primary amino, secondary amino or/and tertiaryamino group(s).

Specific examples include butylamine, octylamine, diethylamine,dibutylamine, methylbutylamine, monoethanolamine, diethanolamine,N-methyl-ethanolamine, triethylamine hydrochloride,N,N-dimethyl-ethanolamine acetate, a mixture of diethyldisulfide andacetic acid, and secondary amine, which is a blocked primary amine, suchas ketimine of aminoethylethanolamine and diketimine ofdiethylenetriamine, etc. One or more amines are available in acombination.

Blocked Isocyanate Curing Agent

As a polyisocyanate for a blocked isocyanate curing agent to be employedin the present invention means a compound having 2 or more of isocyanategroups in a molecule. An example of the polyisocyanate includes any typeof polyisocyanates, such as an aliphatic type, an alicyclic type, anaromatic type, an aromatic-aliphatic type, etc.

Specific example of the polyisocyanate includes aromatic diisocyanatessuch as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI),p-phenylene diisocyanate and naphthalene diisocyanate; aliphaticdiisocyanates having 3 to 12 carbon atoms, such as hexamethylenediisocyanate (HDI), 2,2,4-trimethylhexane diisocyanate and lysinediisocyanate; alicyclic diisocyanates having 5 to 18 carbon atoms, suchas 1,4-cyclohexane diisocyanate (CDI), isophorone diisocyanate (IPDI),4,4′-dicyclohexylmethane diisocyanate (hydrogenated MDI),methylcyclohexane diisocyanate, isopropylidenedicyclohexyl-4,4′-diisocyanate and 1,3-diisocyanatomethylcyclohexane(hydrogenated XDI), hydrogenated TDI and 2,5- or2,6-bis(isocyanatomethyl)-bicyclo[2.2.1]heptane (also called asnorbornane diisocyanate); aliphatic diisocyanates having an aromaticring, such as xylylene diisocyanate (XDI) and tetramethylxylylenediisocyanate (TMXDI); the modified products of these diisocyanates(e.g., urethanated product, carbodiimides, urethodione, urethoimine,biuret and/or isocyanurate modified product), etc. These can be usedalone or 2 or more thereof can be used in combination.

An adduct or a prepolymer which is obtained by reacting a polyisocyanatewith a polyalcohol such as ethylene glycol, propylene glycol,trimethylolpropane or hexanetriol at a ratio NCO/OH of 2 or more may bealso used as a blocked isocyanate curing agent.

The blocking agent is added to a polyisocyanate group, stable at ambienttemperature, but can regenerate a free isocyanate group when it isheated to the dissociation temperature or more.

The blocking agent includes conventional blocking agents, such asε-caprolactam, butyl cellosolve, etc.

The cationic electrodeposition coating composition comprises crosslinkedresin particles as an component, the crosslinked resin particles may beadded to the electrodeposition coating composition at any stage of thepreparing process. Preferably, the crosslinked resin particles may bedirectly added to the previously prepared cationic electrodepositioncoating composition.

Inorganic Pigment

The electrodeposition coating composition used in the present inventionmay contain a conventional inorganic pigment. When it is used in a lowash type, the content of the pigment, in particular, inorganic pigmentmay be reduced or the pigment may not be added. The example of theinorganic pigment includes conventional inorganic pigments, for example,coloring pigments such as titanium white and colcothar; filler pigmentssuch as kaolin, talc, aluminum silicate, calcium carbonate, mica andclay; anticorrosive pigments such as zinc phosphate, iron phosphate,aluminum phosphate, calcium phosphate, zinc phosphite, zinc cyanide,zinc oxide, aluminum tripolyphosphate, zinc molybdate, aluminummolybdate, calcium molybdate, aluminum phosphomolybdate, aluminum zincphosphomolybdate, bismuth oxide, bismuth hydroxide, basic bismuthcarbonate, bismuth nitrate and bismuth sulfate, and the like.

The content of the inorganic pigment is 7% by weight or less, andpreferably 5% by weight or less and more preferably 3% by weight orless, relative to the weight of the solid resin contents in the cationicelectrodeposition coating composition. Further, the “percent weight”relative to the weight of the solid resin contents is called as PWC.When the concentration of the inorganic pigment exceeds 7% by weight,low ash cannot be adequately attained; therefore energy load for theprevention of the sedimentation is increased.

When the pigment is used as a component of the electrodeposition coatingcomposition, these pigments are generally dispersed in an aqueous mediumat a high concentration preliminarily to be a paste (i.e., pigmentdispersed paste). Since the pigment is a powder, it is difficult todisperse the powder at one step in an uniform state at a lowconcentration to be used for the electrodeposition coating composition.Such paste is generally called as a pigment dispersed paste.

The pigment dispersed paste is prepared by dispersing the pigmentstogether with a pigment dispersing resin in an aqueous medium. As thepigment dispersing resin, a cationic or nonionic low molecular weightsurfactant, or a cationic polymer such as a modified epoxy resin havinga quaternary ammonium group and/or a tert-sulfonium group is generallyused. As the aqueous medium, ion exchanged water, water containing asmall amount of an alcohol, and the like are employed.

In general, the pigment dispersing resin is used in an amount of 20 to100 parts by weight based on 100 parts by weight of the pigments (as abasis of the solid content). After the pigment dispersing resin is mixedwith a pigment, the pigment is dispersed using a usual dispersion devicesuch as a ball mill or a sand grind mill until the particle size of thepigment in the mixture becomes a certain uniform particle size to give apigment dispersed paste.

The cationic electrodeposition coating composition used in the presentinvention may contain an organotin compound such as dibutyltin laurate,dibutyltin oxide and dioctyltin oxide; amines such asN-methylmorpholine; and metal salts such as strontium salts, cobaltsalts and copper salts, as a catalyst, in addition to theabove-mentioned components. These can act as a catalyst for dissociationof the blocking agent from the curing agent. The concentration of thecatalyst is preferably 0.1 to 6 parts by weight based on 100 parts byweight of the solid contents in the total of the cationic epoxy resinand the curing agent in the electrodeposition coating composition.

Preparation of Cationic Electrodeposition Coating Composition

The cationic electrodeposition coating composition of the presentinvention can be prepared by dispersing the above-mentioned cationicepoxy resin and a blocked isocyanate curing agent, and if necessary, thecrosslinked resin particles and/or a pigment-dispersed paste and acatalyst, in aqueous medium. Further, the aqueous medium usuallycontains a neutralizing acid for neutralizing the cationic epoxy resinto improve the dispersibility. The neutralizing acid includes inorganicacids or organic acids, such as hydrochloric acid, nitric acid,phosphoric acid, formic acid, acetic acid, lactic acid, sulfamic acidand acetylglycine. The aqueous medium, as used herein, is water or amixture of water with an organic solvent. Ion exchanged water ispreferably used as water. The example of the usable organic solventincludes hydrocarbons (for example, xylene or toluene), alcohols (forexample, methyl alcohol, n-butyl alcohol, isopropyl alcohol,2-ethylhexyl alcohol, ethylene glycol and propylene glycol), ethers (forexample, ethyleneglycol monoethyl ether, ethyleneglycol monobutyl ether,ethyleneglycol monohexyl ether, propyleneglycol monoethyl ether,3-methyl-3-methoxybutanol, diethyleneglycol monoethyl ether anddiethyleneglycol monobutyl ether), ketones (for example, methyl isobutylketone, cyclohexanone, isophorone and acetylacetone), esters (forexample, ethyleneglycol monoethyl ether acetate and ethyleneglycolmonobutyl ether acetate), and a mixture thereof.

The cationic electrodeposition coating composition of the presentinvention may contain the crosslinked resin particle. As a method forthe addition, the crosslinked resin particle may be added at any stageduring the production stages of the electrodeposition coatingcomposition, and it is preferable to directly add the crosslinked resinparticle to the previously produced cationic electrodeposition coatingcomposition.

The amount of the blocked isocyanate curing agent must be adequate forthe curing reaction with a functional group containing an activehydrogen, such as the primary amino group, secondary amino group or ahydroxyl group in the cationic epoxy resin, to provide a good curedcoating. In general, the weight ratio of the solid contents in thecationic epoxy resin to the solid contents in the blocked isocyanatecuring agent is generally within a range of from 90/10 to 50/50 andpreferably 80/20 to 65/35 (epoxy resin/curing agent). The amount ofneutralizing acid is an amount adequate for neutralizing at least 20%and preferably 30 to 60% of the cationic group of the cationic epoxyresin.

The organic solvent is an essential as a solvent for preparing the resincomponents such as the cationic epoxy resin and the blocked isocyanatecuring agent. The complex operations are necessary for completelyremoving the solvent.

Further, when an organic solvent is contained in the cationic epoxyresin as a binder resin component, the fluidity of a coating film duringthe film formation is improved, and the smoothness of the coating filmis improved.

The organic solvent usually contained in the coating compositionincludes ethyleneglycol monobutyl ether, ethyleneglycol monohexyl ether,ethyleneglycol monoethylhexyl ether, propyleneglycol monobutyl ether,dipropyleneglycol monobutyl ether, propyleneglycol monophenyl ether, andthe like.

The cationic electrodeposition coating composition can contain aconventional additive for a coating composition, such as a plasticizer,a surfactant, an antioxidant and an ultraviolet absorbent, in additionto the above-mentioned components.

According to the present invention, in the case of the cationicelectrodeposition coating composition with low solid content, the solidcontent concentration is set at 20% by weight or less. The conventionalcontent is 20% by weight. Specifically, the solid content concentrationof the coating composition is within a range of from preferably 0.5 to9% by weight, and its lower limit value is preferably 2% by weight andmore preferably 4% by weight. On the other hand, its upper limit valueis preferably 7% by weight and more preferably 6% by weight. When thesolid content concentration is less than 0.5% by weight, the appropriatecoating film cannot be formed, and when it is higher than 9% by weight,effects such as the removal of a rinsing step with water and thesimplification of the facilities, these are effects caused by low solidcontent, cannot be obtained in the cationic electrodeposition coatingprocess. Herein, the solid content concentration means a concentrationrelative to the total weight of the pigment(s) component and the resincomponent(s) (also including the crosslinked resin particle component)(as a basis of the solid content) in a cationic electrodepositioncoating composition. Thus, the low solid content has fear of loweringthe electric conductivity of the cationic electrodeposition coatingcomposition. Accordingly, it is preferable to separately add anelectroconductivity controlling agent.

The electroconductivity controlling agent used for the present inventionis not specifically limited so far as it is a material adjusting theelectroconductivity of the cationic electrodeposition coatingcomposition within a desired range, but the electroconductivitycontrolling agent composed of an amino group-containing containingcompound having an amine value of 200 to 500 mmol/100 g is preferable.When the amine value is adjusted for the electroconductivity controllingagent for the cationic electrodeposition coating composition of thepresent invention within the above-mentioned range, it may be anycompound containing an amino group, but generally, theelectroconductivity controlling agent is preferably an amine modifiedepoxy resin or an amine modified acryl resin. Further, theelectroconductivity controlling agent for the cationic electrodepositioncoating composition of the present invention may be neutralized by anacid, if necessary. The amine value is preferably 250 to 450 mmol/100 gand most preferably 300 to 400 mmol/100 g. When the amine value is lessthan 200 mmol/100 g, addition amount necessary for adjusting theelectroconductivity of the cationic electrodeposition coatingcomposition with low solid content concentration to an optimum value isincreased, and there is a fear of loosing anticorrosive property.Further, when it exceeds 500 mmol/100 g, it has defects thatdepositability is lowered and the desired throwing power is notobtained. Further, the adaptability to a zinc steel plate is alsolowered.

The above-mentioned electroconductivity controlling agent includes anamino-group containing compound having from a low molecular weight to ahigh molecular weight, such as a conventional high molecular weightresin such as amine modified epoxy resins and amine modified acrylresins. The example of the low molecular weight compound containing anamino group includes monoethanolamine, diethanolamine,dimethylbutylamine, and the like.

The high molecular weight compound containing an amino group ispreferable, and in particular, the amine modified epoxy resins and theamine modified acryl resins are preferable. The amine modified epoxyresin is obtained by modifying an epoxy group of an epoxy resin with anamine compound. As the epoxy resin, general epoxy resins can be used,and a bisphenol type epoxy resin, a t-butylcathecol type epoxy resin, aphenolnovolak type epoxy resin and a cresolnovolac type epoxy resin,that have a molecular weight of 500 to 20000, are preferable. Amongthese epoxy resins, a phenolnovolak type epoxy resin and a cresolnovolactype epoxy resin are most desirable. In particular, these epoxy resinsare commercially available. Example of the epoxy resin includes aphenolnovolak type epoxy resin DEN-438 manufactured by Dow ChemicalJapan Co., Ltd.; a cresolnovolac type epoxy resin YDCN-703 manufacturedby Tohto Kasei Co., Ltd., etc.

These epoxy resins may be modified with resins such as polyester polyol,polyether polyol and monofunctional alkylphenol. Further, the epoxyresin can extend its chain utilizing a reaction of an epoxy group with adiol or a dicarboxylic acid.

As the amine modified acryl resin, for example, the homopolymer ofdimethylaminoethyl methacrylate that is a monomer containing an aminogroup, or a copolymer of dimethylaminoethyl methacrylate with otherpolymerizable monomer may be used as it is, and it can be obtained bymodifying the glycidyl group of the homopolymer of glycidyl methacrylateor the glycidyl group of a copolymer of glycidyl methacrylate with otherpolymerizable monomer, with an amine compound.

The compound introducing an amino group to the epoxy resin or the acrylresin containing an epoxy group includes primary amines, secondaryamines, tertiary amines, and the like. Their specific example includesbutylamine, octylamine, diethylamine, butylamine, dimethylbutylamine,monoethanolamine, diethanolamine, N-methylethanolamine, triethylaminehydrochloride, N,N-dimethylethanolamine hydrochloride, a mixture ofdiethyldisulfide and acetic acid, and additionally, secondary aminesthat are blocked primary amines such as the diketimine ofaminoethylethanolamine and the diketimine of diethylhydroamine. Aplurality of the amines may be used.

As described above, the number average molecular weight of the aminemodified epoxy resin or the amine modified acryl resin is within a rangeof from preferably 500 to 20000. When the number average molecularweight is smaller than 500, there is a fear of losing anticorrosiveproperty, and although the reason is not clear, the throwing power islowered and the adaptability to a zinc steel plate is lowered. When thenumber average molecular weight is larger than 20000, there is a fear ofproviding the deterioration of the finishing appearance.

The amine modified epoxy resin and/or the amine modified acryl resin canbe also used by being preliminarily neutralized by a neutralizing acid.Acid used for neutralization includes inorganic and organic acids suchas hydrochloric acid, nitric acid, phosphoric acid, sulfamic acid,formic acid, acetic acid and lactic acid.

Application of Cationic Electrodeposition Coating Composition

The above-mentioned cationic electrodeposition coating composition isapplied on an article by an electrodeposition to form anelectrodeposition film. The article includes, but is not specificallylimited to, so far as it is electroconductive, for example, an ironplate, a steel plate, an aluminum plate and a surface treated articlethereof, and a molded article thereof, etc.

The electrodeposition coating with the cationic electrodepositioncoating composition is usually carried out by applying a voltage withina range of from 50 to 450 V between an anode and a cathode which is anarticle to be coated. When the applied voltage is less than 50 V, theelectrodeposition is inadequate, and when it exceeds 450 V, the coatingfilm is broken and the appearance is abnormal. During theelectrodeposition coating, the temperature of the liquid coatingcomposition in a bath is usually adjusted within a range of from 10 to45° C.

The electrodeposition coating includes a step of immersing an article ina cationic electrodeposition coating composition, and a step of applyinga voltage between an anode and a cathode, which is an article to becoated, to form an electrodeposited film. Further, the time for applyinga voltage can be varied depending on the electrodeposition conditionsand generally 2 to 4 min.

The thickness of the resulting electrodeposition film can be generallywithin a range of from 5 to 25 μm. When the film thickness is less than5 μm, there is a fear of inadequate anticorrosive property, and when thefilm thickness exceeds 25 μm, the thickness is sufficient to provide therequired coating film performances. Further, the film resistance of theelectrodeposition film is within a range of from preferably 1000 to 1600kΩ/cm² at a film thickness of 15 p.m. When the film resistance of thecoating film is less than 1000 kΩ/cm², it is a state in which adequateelectric resistance is not obtained, and there is a fear of inferiorthrowing power. Further, when it exceeds 1600 kΩ/cm², there is a fear ofinferior coating film appearance. The film resistance of the coatingfilm is within a range of from more preferably 1100 to 1500 kΩ/cm².

The film resistance value of the coating film can be determined by thefollowing formula according to the residual electric current value (A)of the coating film at the final coating voltage (V).

Film resistance value (FR)=V/A

After the electrodeposition coating, thus obtained electrodepositionfilm as it is or rinsed with water, baked at 120 to 260° C. andpreferably 140 to 220° C. for 10 to 30 min to give a curedelectrodeposition film.

The cured electrodeposition film of the present invention has anexcellent surface smoothness or Ra value as an evaluation index of thesurface smoothness, preferably 0.25 μm or less and more preferably 0.20μm or less. Further, its lower limit value is preferably zero. Ra valueis measured with an evaluation type surface roughness measuring machine(SURFTEST SJ-201P manufactured by Mitsutoyo Corporation) according toJIS-B0601. The smaller Ra value provides the better coating filmappearance having a suppressed concavo-convex.

Further, in the present invention, there is provided a method forestablishing both of the smoothness and the edge coatability of thecationic electrodeposition coating composition characterized in that thecationic electrodeposition coating composition comprises the crosslinkedresin particles having an average particle size within a range of from1.0 to 3.0 μm and a thermal softening temperature within a range of from120 to 180° C. in a process of forming a cationic electrodeposition filmby immersing an article in the cationic electrodeposition coatingcomposition and applying a voltage. Further, in the present invention,even if the cationic electrodeposition coating composition is low solidtype and low ash type, the ability of preventing the sedimentation ofthe solid contents in the electrodeposition coating composition can beimproved by adding the specific crosslinked resin particle in thecationic electrodeposition coating composition as an additive, and bothof the surface smoothness and edge coatability can be established. Theamount in that case is within a range of from 3 to 15% by weightrelative to the weight of the solid contents in the cationicelectrodeposition coating composition.

EXAMPLES

The present invention is further specifically described below accordingto the Examples, but the present invention is not limited to theseExamples. Further, the term “part(s)” represent(s) part(s) by weightunless otherwise noticed.

Production Example 1A Production of Blocked Isocyanate Curing Agent

In a flask equipped with a stirrer, a cooler, a nitrogen charging tube,a thermometer and a dropping funnel, 199 parts of the trimer ofhexamethylene diisocyanate (CORONATE HX: manufactured by NipponPolyurethane Industry Co., Ltd.), 32 parts of methyl isobutyl ketone and0.03 part of dibutyltin dilaurate were weighed, and 87.0 parts of methylethyl ketone oxime was added dropwise thereto from the dropping funnelover 1 hr, while stirring and bubbling nitrogen. Temperature was raisedfrom 50° C. to 70° C. Thereafter, the reaction was continued for 1 hr,and the reaction was continued until the absorption of NCO group wasextinguished by an infrared spectrometer. Then, 0.74 part of n-butanoland 39.93 parts of methyl isobutyl ketone were added to prepare amixture with a non-volatile content of 80%.

Production Example 2A Production of Amine Modified Epoxy Resin Emulsion

In a flask equipped with a stirrer, a cooler, a nitrogen charging tubeand a dropping funnel, 71.34 parts of 2,4-/2,6-tolylene diisocyanate(80/20% by weight), 111.98 parts of methyl isobutyl ketone and 0.02 partof dibutyltin dilaurate were weighed, and 14.24 parts of methanol wasadded dropwise from the dropping funnel over 30 min while stirring andbubbling nitrogen. The temperature was raised from room temperature to60° C. by exothermic heat. Then, after the reaction was continued for 30minutes, 46.98 parts of ethyleneglycol mono-2-ethylhexyl ether was addeddropwise from the dropping funnel over 30 min. Temperature was raised to70 to 75° C. by exothermic heat. After the reaction was continued for 30min, 41.25 parts of the adduct of bisphenol A with propylene oxide (5mol) (BP-5P manufactured by Sanyo Kasei Co., Ltd.) was added to themixture, temperature was raised to 90° C., and the reaction wascontinued while measuring IR spectrum until NCO group was extinguished.

Successively, 475.0 parts of a bisphenol A type epoxy resin having anepoxy equivalent of 475 (YD-7011R manufactured by Tohto Kasei Co., Ltd.)was added to be homogeneously dissolved, and then temperature was raisedfrom 130° C. to 142° C., and water was removed from the reaction systemby azeotrope with MIBK. After the reaction mixture was cooled to 125°C., 1.107 parts of benzyldimethylamine was added, and reaction offorming an oxazolidone ring by demethanolation was carried out. Thereaction was continued until the epoxy equivalent was 1140.

Then, the mixture was cooled to 100° C., and 24.56 parts ofN-methylethanolamine, 11.46 parts of diethanolamine and 26.08 parts ofketimine of aminoethylethanolamine (78.8% methyl isobutyl ketonesolution) were added thereto to be reacted at 110° C. for 2 hrs. Then,20.74 parts of ethyleneglycol mono-2-ethylhexyl ether and 12.85 parts ofmethyl isobutyl ketone were added to the mixture to be diluted, andnon-volatile content was adjusted to 82%. Number average molecularweight (by GPC method) was 1380 and amine equivalent was 94.5 meq/100 g.

145.11 Parts of ion exchanged water and 5.04 parts of acetic acid wereweighed in another container, a mixture of 320.11 parts (75.0 parts assolid content) of the above-mentioned amine modified epoxy resin and190.38 parts (25.0 parts as solid content) of the blocked isocyanatecuring agent of Production Example 1A, which was heated to 70° C., wasadded thereto dropwise gradually, and the mixture was stirred to behomogeneously dispersed. Then, ion exchanged water was added thereto toadjust the solid content to 36%.

Production Example 3A Production of Pigment Dispersing Resin

In a flask equipped with a stirrer, a cooler, a nitrogen charging tube,a thermometer and a dropping funnel, 382.20 parts of a bisphenol A typeepoxy resin having an epoxy equivalent of 188 (under product name:DER-331J) and 111.98 parts of bisphenol A were weighed, temperature wasraised to 80° C. to dissolve the mixture homogeneously, then 1.53 partsof 1% solution of 2-ethyl-4-methylimidazole was added, and reaction wascarried out at 170° C. for 2 hrs. After cooling the mixture to 140° C.,196.50 parts of 2-ethylhexanol-half blocked isophorone diisocyanate(non-volatile content: 90%) was added to the mixture, and the reactionwas carried out until NCO group was extinguished. Thereto, 205.00 partsof dipropylene glycol monobutyl ether was added, successively, 408.00parts of 1-(2-hydroxyethylthio)-2-propanol and 134.00 parts ofdimethylol propionate were added, 144.00 parts of ion exchanged waterwas added, and the mixture was reacted at 70° C. The reaction wascontinued until acid value was 5 or less. The obtained resin varnishobtained was diluted to a non-volatile content of 35% with 1150.50 partsof ion exchanged water.

Production Example 4A Production of Pigment Dispersed Paste

In a sand grind mill, 120 parts of the pigment dispersing resin varnishobtained in Production Example 3A, 100.0 parts of kaolin, 92 parts oftitanium dioxide, 8.0 parts of dibutyltin oxide and 184 parts of ionexchanged water were charged, and dispersed until particle size was 10μm or less to obtain a pigment dispersed paste (solid content: 48%).

Production Example 5A Production of Crosslinked Resin Particles

In a reaction container, 120 parts of butylcellosolve was charged, andit was heated to 120° C. with stirring. Thereto, a solution which was amixture of 2 parts of t-butylperoxy-2-ethylhexanoate and 10 parts ofbutylcellosolve, and a monomer mixture containing 15 parts of glycidylmethacrylate, 50 parts of 2-ethylhexyl methacrylate, 20 parts of2-hydroxyethyl methacrylate and 15 parts of n-butyl methacrylate whoseSP value was 10.1 were added dropwise over 3 hrs. After aging for 30min, a solution which was a mixture of 0.5 part oft-butylperoxy-2-ethylhexanoate and 5 parts of butylcellosolve was addeddropwise for 30 min, and after aging for 2 hrs, the mixture was cooled.Quartenization was carried out by adding 7 parts ofN,N-dimethylaminoethanol and 15 parts of 50% aqueous lactic acidsolution to the mixture with heating at 80° C. and stirring. When acidvalue was 1 or less and the rising of viscosity was stopped, heating wasterminated to obtain an acryl resin having an ammonium group. The numberof the ammonium group per one molecule of the acryl resin having anammonium group was 6.0.

To the reaction container, 120 parts of the acryl resin having anammonium group and 270 parts of deionized water were added, and themixture was stirred with heating at 75° C. Thereto, the 100% neutralizedaqueous solution of 1.5 parts of2,2′-azobis(2-(2-imidazolin-2-yl)propane) with acetic acid was addeddropwise over 5 min. After aging for 5 min, 30 parts of methylmethacrylate was added dropwise over 5 min. After aging further 5 min,an α,β-ethylenically unsaturated monomer mixture containing 170 parts ofmethyl methacrylate, 40 parts of styrene, 30 parts of n-butylmethacrylate, 5 parts of glycidyl methacrylate and 30 parts ofneopentylglycol dimethacrylate was added to a solution which was amixture of 170 parts of the acryl resin having an ammonium group and 250parts of deionized water with stirring to give a pre-emulsion, and thepre-emulsion was added dropwise over 40 min. After aging for 60 min, itwas cooled to give a dispersion of crosslinked resin particles 1. Thenon-volatile content in the dispersion of the crosslinked resinparticles was 35%, pH was 5.0 and an average particle size was 100 nm.

Production Example 6A Production of Non-Crosslinked Resin Particles

2 Parts of lauroyl peroxide was dissolved in a solution which was amixture of 104 parts of styrene, 20 parts of 2-ethylhexyl methacrylateand 76 parts of lauryl methacrylate. This was added in 497 parts ofaqueous solution in which 8 parts of polyvinyl alcohol (GOUSENOL GH-17,manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) wasdissolved in deionized water, while stirring, and a dispersion wasproduced at 3500 rpm with a HOMOMIC LINE FLOW 30 type machine (highspeed dispersing machine manufactured by TOKUSYU KIKA KOUGYOU Co.,Ltd.).

The suspension polymerization of the suspension was carried out at astirring speed of 150 rpm and a reaction temperature of 81 to 83° C.over 5 hrs using a usual batch wise reaction container, and aftercooling, the resulted dispersion was filtered with a 200 mesh net togive non-crosslinked resin particles. The non-volatile content in thedispersion of the non-crosslinked resin particles was 30% and an averageparticle size was 3 μm.

Example 1A

2222 Parts of the emulsion obtained in Production Example 2A, 417 partsof the pigment dispersed paste obtained in Production Example 4A and2361 parts of ion exchanged water were mixed to give a cationicelectrodeposition coating composition in which PWC was 16.5%, thecontent of the crosslinked resin particles was zero % by weight, and thesolid content was 20% by weight.

Comparative Example 1A

738 Parts of the emulsion obtained in Production Example 2A, 4 parts ofdibutyltin oxide and 4598 parts of ion exchanged water were mixed togive a cationic electrodeposition coating composition in which PWC was0%, the content of the crosslinked resin particles was zero % by weight,and the solid content was 5% by weight.

Comparative Example 2A

702 Parts of the emulsion obtained in Production Example 2A, 38 parts ofthe crosslinked resin particles obtained in Production Example 5A, 4parts of dibutyltin oxide and 4596 parts of ion exchanged water weremixed to give a cationic electrodeposition coating composition in whichPWC was 0%, the content of the crosslinked resin particles was 5% byweight, and the solid content was 5% by weight.

Comparative Example 3A

665 Parts of the emulsion obtained in Production Example 2A, 76 parts ofthe crosslinked resin particles obtained in Production Example 5A, 4parts of dibutyltin oxide and 4596 parts of ion exchanged water weremixed to give a cationic electrodeposition coating composition in whichPWC was 0%, the content of the crosslinked resin particles was 10% byweight, and the solid content was 5% by weight.

Comparative Example 4A

665 Parts of the emulsion obtained in Production Example 2A, 89 parts ofthe non-crosslinked resin particles obtained in Production Example 6A, 4parts of dibutyltin oxide and 4582 parts of ion exchanged water weremixed to give a cationic electrodeposition coating composition in whichPWC was 0%, the content of the non-crosslinked resin particles was 10%by weight, and the solid content was 5% by weight.

Comparative Example 5A

389 Parts of the emulsion obtained in Production Example 2A, 125 partsof the pigment dispersed paste obtained in Production Example 4A and3486 parts of ion exchanged water were mixed to give a cationicelectrodeposition coating composition in which PWC was 25%, the contentof the crosslinked resin particles was 0% by weight, and the solidcontent was 5% by weight.

Example 2A

702 Parts of the emulsion obtained in Production Example 2A, 42 parts ofthe crosslinked resin particles (crosslinked resin particles in whichmethyl methacrylate was a main component; TAFTIC® F-200: manufactured byToyobo Co., Ltd.), 4 parts of dibutyltin oxide and 4592 parts of ionexchanged water were mixed to give a cationic electrodeposition coatingcomposition in which PWC was 0%, the content of the crosslinked resinparticles was 5% by weight, and the solid content was 5% by weight.

Example 3A

665 Parts of the emulsion obtained in Production Example 2A, 84 parts ofthe crosslinked resin particles (crosslinked resin particles in whichmethyl methacrylate was a main component; TAFTIC® F-200: manufactured byToyobo Co., Ltd.), 4 parts of dibutyltin oxide and 4587 parts of ionexchanged water were mixed to give a cationic electrodeposition coatingcomposition in which PWC was 0%, the content of the crosslinked resinparticles was 10% by weight, and the solid content was 5% by weight.

Example 4A

628 Parts of the emulsion obtained in Production Example 2A, 127 partsof the crosslinked resin particles (crosslinked resin particles in whichmethyl methacrylate was a main component; TAFTIC® F-200: manufactured byToyobo Co., Ltd.), 4 parts of dibutyltin oxide and 4581 parts of ionexchanged water were mixed to give a cationic electrodeposition coatingcomposition in which PWC was 0%, the content of the crosslinked resinparticles was 15% by weight, and the solid content was 5% by weight.

Example 5A

628 Parts of the emulsion obtained in Production Example 2A, 40 parts ofthe crosslinked resin particles (crosslinked resin particles in whichStyrene monomer was a main component; CHEMISNOW SX500H: manufactured bySoken Chemical & Engineering Co., Ltd., which had an average particlesize of 3 μm), 4 parts of dibutyltin oxide and 4668 parts of ionexchanged water were mixed to give a cationic electrodeposition coatingcomposition in which PWC was 0%, the content of the crosslinked resinparticles was. 15% by weight, and the solid content was 5% by weight.

Example 6A

567 Parts of the emulsion obtained in Production Example 2A, 54 parts ofthe pigment dispersed paste obtained in Production Example 4A, 40 partsof crosslinked resin particles (crosslinked resin particles in whichstyrene monomer was a main component; CHEMISNOW SX500H: manufactured bySoken Chemical & Engineering Co., Ltd., which had an average particlesize of 3 μm) and 4739 parts of ion exchanged water were mixed to give acationic electrodeposition coating composition in which PWC was 8%, thecontent of the crosslinked resin particles was 15% by weight, and thesolid content was 5% by weight.

With respect to thus prepared cationic electrodeposition coatingcompositions, the loss elasticity modulus at 80° C. and the storageelasticity modulus at 140° C. in dynamic viscoelasticities, and thesmoothness and the edge coatability were evaluated by the methods below.

Measurement of Loss Elasticity Modulus and Storage Elasticity Modulus ofElectrodeposition Film

A tin plate was immersed in the cationic electrodeposition coatingcomposition prepared as described above. An electrodeposition film wasformed by applying a voltage so that the film thickness after baking was15 μm, and then the plate was rinsed with water to remove the excessiveelectrodeposition coating composition. Then, after removing moisture,without drying, the plate having the uncured coating film wasimmediately taken out to prepare a sample. The dynamic viscoelasticitiesof the sample were measured depending on the temperature withRheosol-G3000 (manufactured by UBM Corporation) that was a rotationaltype dynamic viscoelasticity measurement device (under measurementconditions of a strain of 0.5 deg and a frequency of 0.02 Hz), whereinthe sample was set, and the measurement temperature was kept at 50° C.After starting the measurement, the measurement of the viscosity of thecoating film was carried out when the electrodeposition film wasuniformly spread in a cone plate.

Evaluation of Appearance (Smoothness) of Electrodeposition Film

Evaluation of an appearance of an electrodeposition film was carried outby measuring an arithmetic average roughness (Ra) on a roughness curve.A cold rolling steel plate treated with zinc phosphate was immersed inthe cationic electrodeposition coating composition prepared as describedabove. An uncured electrodeposition film obtained by applying a voltage,so that the film thickness after baking was 15 μm, was baked at 160° C.for 10 min. Then, the Ra value of the cured electrodeposition film wasmeasured with an evaluation type surface roughness measuring machine(SURFTEST SJ-201 P manufactured by Mitsutoyo Corporation) in accordancewith JIS-B0601. Measurement was repeated 7 times on the sample withcut-offs in a width of 2.5 mm (partition number was 5), and the Ra valuewas an average of the measured values without the maximum and minimumvalues. The results are shown in Table 1. It can be understood that thesmaller Ra value provides the better coating film appearance with asuppressed concavo-convex.

Evaluation Method for Edge Coatability

A cutter knife blade (LB-50K manufactured by OLFA Co.) treated with zincphosphate, as an article to be coated, was immersed into a cationicelectrodeposition coating composition. A voltage was applied between ananode and a cathode, which is the above-described article, to give anelectrodeposition film, wherein the above-mentioned electrodepositionconditions on the applying voltage and time were adjusted so that thethickness of the film electrodeposited on the knife blade was 15 μm. Theresulted electrodeposition film was rinsed with water, and then baked at160° C. for 10 min to give a cured electrodeposition film.

The cutter knife blade coated with the electrodeposition film was foldedoff in the center. The thickness of the electrodeposition film appliedon the cutter knife blade was measured with a digital microscope(VH-8000 manufactured by KEYENCE Corporation) in a distance (30 microns)from the (sharp) edge of the cutter knife blade. FIG. 9 schematicallyshows the point of the cutter knife blade in the distance, 30 microns,from the edge of the blade.

TABLE 1 Comp. Comp. Comp. Comp. Comp. Ex. 1A Ex. 2A Ex. 3A Ex. 4A Ex. 5AEx. 1A Resin particle None Production Production Production None NoneEx. 5A: Ex. 5A: Ex. 6A: Crosslinked Crosslinked Non-crosslinked AverageAverage Average particle particle particle size: size: 0.1 μm size: 0.1μm 1 to 5 μm Resin particle content (%) None 5 10 10 0 None Ash(pigment) content (%) 0 0 0 0 25 16.5 Melt Loss 23 156 228 50 152 89viscosity elasticity modulus G″ (dyn/cm²) Storage 21 73 110 50 136 155elasticity modulus G′ (dyn/cm²) Evaluation Smoothness 0.19 0.30 0.370.20 0.33 0.18 results Ra (C/O = 2.5) Edge 3.6 6.0 8.3 5.1 8.0 7.9coatability (μm) Ex. 2A Ex. 3A Ex. 4A Ex. 5A Ex. 6A Resin particleTAFTIC TAFTIC TAFTIC CHEMISNOW CHEMISNOW F-200: F-200: F-200: SX500HSX500H Average Average Average Average Average particle particleparticle particle size: particle size: size: size: size: 3 μm 3 μm 2 μm2 μm 2 μm Resin particle content (%) 5 10 15 15 15 Ash (pigment) content(%) 0 0 0 0 12 Melt Loss 88 113 142 121 144 viscosity elasticity modulusG″ (dyn/cm²) Storage 85 107 125 116 136 elasticity modulus G′ (dyn/cm²)Evaluation Smoothness 0.21 0.21 0.23 0.24 0.24 results Ra (C/O = 2.5)Edge 7.5 7.8 8.2 8.1 8.3 coatability (μm)

As seen in the Table 1, it is understood that the electrodepositioncoating compositions having the loss elasticity modulus (G″) and thestorage elasticity modulus (G′) within the defined ranges as dynamicviscoelasticities provide excellent performances in the smoothness andthe edge coatability. Specifically, in the Comparative Example 1A, theelectrodeposition coating composition having a storage elasticitymodulus (G′) out of the defined range in the present invention does notprovide a good edge coatability. In the Comparative Example 2A, theelectrodeposition coating composition comprising the crosslinked resinparticles of the Production Example 5A and having a loss elasticitymodulus (G″) and a storage elasticity modulus (G′), both of which areout of the defined ranges in the present invention, does not provide agood smoothness and a good edge coatability. Similar to the ComparativeExample 2A, in the Comparative Example 3A, the electrodeposition coatingcomposition comprising the crosslinked resin particles of the ProductionExample 5A, wherein the crosslinked resin particles have a small averageparticle size of 100 nm, and having a loss elasticity modulus (G″) outof the defined range in the present invention, does provide a poorsmoothness. In the Comparative Example 4A, the electrodeposition coatingcomposition comprising the non-crosslinked resin particles, and having astorage elasticity modulus (G′) out of the defined range in the presentinvention, does provide a poor edge coatability. In the ComparativeExample 5A, the electrodeposition coating composition comprising theinorganic pigment without any resin particles, and having a losselasticity modulus (G″) out of the defined range in the presentinvention, does not provide a good smoothness. In the Example 1A, theelectrodeposition coating composition comprising the pigment of theProduction Example 4A, wherein all the parameters are within the presentdefined ranges, provides an excellent smoothness and an excellent edgecoatability. In the Examples 2A to 6A, each of the electrodepositioncoating compositions comprises a certain particle, wherein the storageelasticity modulus (G′) and the loss elasticity modulus (G″) arecontrolled within the present defined ranges, and provides an excellentsmoothness and an excellent edge coatability.

Production Example 1B Production of Blocked Isocyanate Curing Agent

In a flask equipped with a stirrer, a cooler, a nitrogen charging tube,a thermometer and a dropping funnel, 199 parts of the trimer ofhexamethylene diisocyanate (CORONATE HX: manufactured by NipponPolyurethane Industry Co., Ltd.), 32 parts of methyl isobutyl ketone and0.03 part of dibutyltin dilaurate were weighed, and 87.0 parts of methylethyl ketone oxime was added dropwise thereto from the dropping funnelover 1 hr while stirring and bubbling nitrogen. Temperature was raisedfrom 50° C. to 70° C. initially. Thereafter, the reaction was continuedfor 1 hr, and the reaction was continued until the absorption of NCOgroup was extinguished by an infrared spectrometer. Then, 0.74 part ofn-butanol and 39.93 parts of methyl isobutyl ketone were added toprepare a mixture with a non-volatile content of 80%.

Production Example 2B Production of Emulsion Containing Amine ModifiedEpoxy Resin and Blocked Isocyanate Curing Agent

In a flask equipped with a stirrer, a cooler, a nitrogen charging tubeand a dropping funnel, 71.34 parts of 2,4-/2,6-tolylene diisocyanate(80/20% by weight), 111.98 parts of methyl isobutyl ketone and 0.02 partof dibutyltin dilaurate were weighed, and 14.24 parts of methanol wasadded dropwise from the dropping funnel over 30 min while stirring andbubbling nitrogen. The temperature was raised from room temperature to60° C. by exothermic heat. Then, after the reaction was continued for 30minutes, 46.98 parts of ethyleneglycol mono-2-ethylhexyl ether was addeddropwise from the dropping funnel over 30 min. Temperature was raised to70 to 75° C. by exothermic heat. After the reaction was continued for 30min, 41.25 parts of the adduct of bisphenol A with propylene oxide (5mol) (BP-5P manufactured by Sanyo Kasei Co., Ltd.) was added to themixture, temperature was raised to 90° C., and the reaction wascontinued while measuring IR spectrum until NCO group was extinguished.

Successively, 475.0 parts of a bisphenol A type epoxy resin having anepoxy equivalent of 475 (YD-7011 R manufactured by Tohto Kasei Co.,Ltd.) was added to be homogeneously dissolved, and then, temperature wasraised from 130° C. to 142° C., and water was removed from the reactionsystem by azeotrope with MIBK. After the reaction mixture was cooled to125° C., 1.107 parts of benzyldimethylamine was added and reaction offorming an oxazolidone ring by demethanolation was carried out. Thereaction was continued until the epoxy equivalent was 1140.

Then, the mixture was cooled to 100° C., and 24.56 parts ofN-methylethanolamine, 11.46 parts of diethanolamine and 26.08 parts ofketimine of aminoethylethanolamine (78.8% methyl isobutyl ketonesolution) were added thereto to be reacted at 110° C. for 2 hrs Then,20.74 parts of ethyleneglycol mono-2-ethylhexyl ether and 12.85 parts ofmethyl isobutyl ketone were added to the mixture to be diluted, andnon-volatile content was adjusted to 82%. An amine modified epoxy resinin which number average molecular weight (by GPC method) was 1380 andamine equivalent was 94.5 meq/100 g was obtained.

145.11 Parts of ion exchanged water and 5.04 parts of acetic acid wereweighed in another container, a mixture of 320.11 parts (75.0 parts assolid content) of the above-mentioned amine modified epoxy resin and190.38 parts (25.0 parts as solid content) of the blocked isocyanatecuring agent of Production Example 1B, which was heated to 70° C., wasadded thereto dropwise gradually, and the mixture was stirred to behomogeneously dispersed. Then, ion exchanged water was added thereto toadjust the solid content to 36%.

Production Example 3B Production of Pigment Dispersing Resin Varnish

In a flask equipped with a stirrer, a cooler, a nitrogen charging tube,a thermometer and a dropping funnel, 382.20 parts of a bisphenol A typeepoxy resin having an epoxy equivalent of 188 (under product name:DER-331J) and 111.98 parts of bisphenol A were weighed, temperature wasraised to 80° C. to dissolve the mixture homogeneously, then 1.53 partsof 1% solution of 2-ethyl-4-methylimidazole was added, and reaction wascarried out at 170° C. for 2 hrs. After cooling the mixture to 140° C.,196.50 parts of 2-ethylhexanol-half blocked isophorone diisocyanate(non-volatile content: 90%) was added to the mixture, and the reactionwas carried out until NCO group was extinguished. Thereto, 205.00 partsof dipropylene glycol monobutyl ether was added, successively, 408.00parts of 1-(2-hydroxyethylthio)-2-propanol and 134.00 parts ofdimethylol propionate were added, 144.00 parts of ion exchanged waterwas added, and the mixture was reacted at 70° C. The reaction wascontinued until acid value was 5 or less. The obtained resin varnish wasdiluted to a non-volatile content of 35% with 1150.50 parts of ionexchanged water.

Production Example 4B Production of Pigment Dispersed Paste

In a sand grind mill, 120 parts of the pigment dispersing resin varnishobtained in Production Example 3B, 100.0 parts of kaolin, 92.0 parts oftitanium dioxide, 8.0 parts of dibutyltin oxide and 184 parts of ionexchanged water were charged, and dispersed until particle size was 10μm or less to obtain a pigment dispersed paste (solid content: 48%).

Production Example 5B Production of Crosslinked Resin Particles forComparison

In a reaction container, 120 parts of butylcellosolve was charged, andit was heated to 120° C. with stirring. Thereto, a solution which was amixture of 2 parts of t-butylperoxy-2-ethylhexanoate, and 10 parts ofbutylcellosolve, and a monomer mixture containing 15 parts of glycidylmethacrylate, 50 parts of 2-ethylhexyl methacrylate, 20 parts of2-hydroxyethyl methacrylate, and 15 parts of n-butyl methacrylate wereadded dropwise over 3 hrs. After aging for 30 min, a solution which wasa mixture of 0.5 part of t-butylperoxy-2-ethyl hexanoate and 5. parts ofbutylcellosolve was added dropwise for 30 min, and after aging for 2hrs, the mixture was cooled. Thereto, 7 parts ofN,N-dimethylaminoethanol and 15 parts of 50% aqueous lactic acidsolution were added to the mixture with heating at 80° C. and stirring.When an acid value was 1 or less and the rising of viscosity wasstopped, heating was terminated to obtain an acryl resin having anammonium group. The number of the ammonium group per one molecule of theacryl resin having an ammonium group was 6.0.

To the reaction container, 120 parts of the acryl resin having anammonium group and 270 parts of deionized water were added, and themixture was stirred with heating at 75° C. Thereto, the 100% neutralizedaqueous solution of 1.5 parts of2,2′-azobis(2-(2-imidazolin-2-yl)propane) with acetic acid was addeddropwise over 5 min. After aging for 5 min, 30 parts of methylmethacrylate was added dropwise over 5 min. After aging further 5 min,an ethylenically unsaturated monomer mixture containing 170 parts ofmethyl methacrylate, 40 parts of styrene, 30 parts of n-butylmethacrylate, 5 parts of glycidyl methacrylate and 30 parts ofneopentylglycol dimethacrylate was added to a solution which was amixture of 170 parts of the acryl resin having an ammonium group and 250parts of deionized water with stirring to give a pre-emulsion, and thepre-emulsion was added dropwise over 40 min. After aging for 60 min, itwas cooled to give a dispersion of crosslinked resin particles 1. Thenon-volatile content in the dispersion of the crosslinked resinparticles was 35%, pH was 5.0 and an average particle size was 0.1 μm.Herein, the average particle size was measured according to thefollowings.

The average particle size of the resin particles was measured by agranular particle transmission measurement method with MICROTRAC9340UPAmanufactured by Nikkiso Co., Ltd. Further, the particle sizedistribution of the resin particles was measured by the measurementdevice, and an average particle size at a cumulative relative frequency[F(x)=0.5] was calculated from the measurement values. In thesemeasurements and calculations, the employed refractive index of asolvent (water) was 1.33, and the employed refractive index of the resincontent was 1.59.

Production Example 6B

In a flask equipped with a reflux cooler and a stirrer, 295 parts ofmethyl isobutyl ketone (hereinafter, abbreviated as “MIBK”), 37.5 partsof methylethanolamine and 52.5 parts of diethanolamine were charged, andthe mixture was kept at 100° C. with stirring. Thereto, 205 parts ofcresol novolac epoxy resin (under product name; YDCN-703, manufacturedby Tohto Kasei Co., Ltd.) was gradually added. After complete addition,the reaction was carried out for 3 hrs. When its molecular weight wasmeasured, it was 2100. When the amine value (MEQ(B)) of the aminomodified resin was measured, it was 340 mmol/100 g.

5.5 Parts of formic acid and 1254.5 parts of deionized water were addedto 140 parts of the amino modified resin solution, and the mixture wasstirred for 30 min while keeping it at 80° C. The organic solvent wasremoved under reduced pressure to give anelectroconductivity-controlling agent with a solid content of 5.0%.

Example 1B

628 Parts of the emulsion obtained in Production Example 2B, 127 partsof the crosslinked resin particles (crosslinked resin particles in whichmethyl methacrylate monomer was a main component; GM-0105 (under productname): manufactured by GANZ Chemical Co., Ltd.), 4 parts of dibutyltinoxide and 4581 parts of ion exchanged water were mixed to give acationic electrodeposition coating composition in which PWC was 0%, thecontent of the resin particles was 15% by weight, and the solid contentwas 5% by weight.

Example 2B

628 Parts of the emulsion obtained in Production Example 2B, 127 partsof the crosslinked resin particles (crosslinked resin particles in whichmethyl methacrylate was a main component; TAFTIC®F-200: manufactured byToyobo Co., Ltd.), 4 parts of dibutyltin oxide and 4581 parts of ionexchanged water were mixed to give a cationic electrodeposition coatingcomposition in which PWC was 0%, the content of the crosslinked resinparticles was 15% by weight, and the solid content was 5% by weight.

Example 3B

561 Parts of the emulsion obtained in Production Example 2B, 19 parts ofthe pigment dispersed paste obtained in Production Example 4B, 114 partsof the crosslinked resin particles (crosslinked resin particles in whichmethyl methacrylate monomer was a main component; TAFTIC® F-200:manufactured by Toyobo Co., Ltd.), 3 parts of dibutyltin oxide and 4303parts of ion exchanged water were mixed to give a cationicelectrodeposition coating composition in which PWC was 3%, the contentof the crosslinked resin particles was 10% by weight, and the solidcontent was 5% by weight.

Example 4B

578 Parts of the emulsion obtained in Production Example 2B, 360 partsof the electroconductivity-controlling agent (solid content: 5%)obtained in Production Example 6B, 127 parts of the crosslinked resinparticles (crosslinked resin particles in which methyl methacrylatemonomer was a main component; TAFTIC® F-200: manufactured by Toyobo Co.,Ltd.), 4 parts of dibutyltin oxide and 4331 parts of ion exchanged waterwere mixed to give a cationic electrodeposition coating composition inwhich PWC was 0%, the content of the crosslinked resin particles was 15%by weight, and the solid content was 5% by weight.

Comparative Example 1B

2444 Parts of the emulsion obtained in Production Example 2B, 250 partsof the pigment dispersed paste obtained in Production Example 4B, 2346parts of ion exchanged water and 10 parts of dibutyltin oxide were mixedto give a cationic electrodeposition coating composition in which thesolid content was 20% by weight.

Comparative Example 2B

738 Parts of the emulsion obtained in Production Example 2B, 4 parts ofdibutyltin oxide and 4598 parts of ion exchanged water were mixed togive a cationic electrodeposition coating composition in which PWC was0% (ash content was not contained), the content of the crosslinked resinparticles was 0% by weight, and the solid content was 5% by weight.

Comparative Example 3B

702 Parts of the emulsion obtained in Production Example 2B, 38 parts ofthe crosslinked resin particles obtained in Production Example 5B, 4parts of dibutyltin oxide and 4596 parts of ion exchanged water weremixed to give a cationic electrodeposition coating composition in whichPWC was 0%, the content of the crosslinked resin particles was 5% byweight, and the solid content was 5% by weight.

Comparative Example 4B

665 Parts of the emulsion obtained in Production Example 2B, 76 parts ofthe crosslinked resin particles obtained in Production Example 5B, 4parts of dibutyltin oxide and 4596 parts of ion exchanged water weremixed to give a cationic electrodeposition coating composition in whichPWC was 0%, the content of the crosslinked resin particles was 10% byweight, and the solid content was 5% by weight.

Comparative Example 5B

579 Parts of the emulsion obtained in Production Example 2B, 38-parts ofthe crosslinked resin particles (crosslinked resin particles in whichstyrene monomer was a main component; CHEMISNOW® SX130M: manufactured bySoken Chemical & Engineering Co., Ltd.), 4 parts of dibutyltin oxide and4388 parts of ion exchanged water were mixed to give a cationicelectrodeposition coating composition in which PWC was 0%, the contentof the crosslinked resin particles was 15% by weight and the solidcontent was 5% by weight.

With respect to thus prepared cationic electrodeposition coatingcompositions, the loss elasticity modulus at 80° C. and the storageelasticity modulus at 140° C. in dynamic viscoelasticities, and thesmoothness and the edge coatability, and the like were evaluated by themethods below.

Measurement of Loss Elasticity Modulus and Storage Elasticity Modulus ofElectrodeposition Film

A tin plate was immersed in the cationic electrodeposition coatingcomposition prepared as described above. An electrodeposition film wasformed by applying a voltage so that the film thickness after baking was15 μm, and then the plate was rinsed with water to remove the excessiveelectrodeposition coating composition. Then, after removing moisture,without drying, the plate having the uncured coating film wasimmediately taken out to prepare a sample. The dynamic viscoelasticitiesof the sample, i.e., storage elasticity modulus (G′) and loss elasticitymodulus (G″) were measured depending on the temperature withRheosol-G3000 (manufactured by UBM Corporation) that was a rotationaltype dynamic viscoelasticity measurement device (under measurementconditions: a strain of 0.5 deg; a frequency of 0.02 Hz, and a raisingrate of 2.0° C./min).

Evaluation of Appearance (Smoothness) of Electrodeposition Film

Evaluation of an appearance of an electrodeposition film was carried outby measuring an arithmetic average roughness (Ra) on a roughness curve.A cold rolling steel plate treated with zinc phosphate was immersed in acationic electrodeposition coating composition. An uncuredelectrodeposition film obtained by applying a voltage, so that the filmthickness after baking was 15 μm, was baked at 160° C. for 10 min. Then,the Ra value of the uncured electrodeposition film was measured with anevaluation type surface roughness measuring machine (SURFTEST SJ-201 Pmanufactured by Mitsutoyo Corporation) in accordance with JIS-B0601.Measurement was repeated 7-times on the sample with cut-offs in a widthof 2.5 mm (partition number was 5), and the Ra value was an average ofthe measured values without the maximum and minimum values. The resultsare shown in Tables 2 and 3. It can be understood that the smaller Ravalue provides the better coating film appearance with a suppressedconcavo-convex. Specifically, an acceptable range of the Ra value is nomore than 0.25 μm.

Evaluation Method for Sedimentability (Planer Appearance)

A cold rolling steel plate treated with zinc phosphate was immersed intoeach of the cationic electrodeposition coating compositions obtained inProduction Examples and Comparative Examples, in a horizontal direction,and an uncured electrodeposition film was obtained by applying a voltageso that the film thickness after baking was 15 μm. After baking of theuncured electrodeposition film at 160° C. for 10 min, the arithmeticaverage roughness (Ra) on a roughness curve was measured in a similarmanner to that in the above-mentioned evaluation for an appearance of anelectrodeposition film with a surface roughness measuring machine.

If sedimentability of an electrodeposition coating composition isinferior, a horizontal (planar) appearance (smoothness in a horizontaldirection) of the electrodeposition film is deteriorated in comparisonwith a vertical appearance (smoothness in a vertical direction) of theelectrodeposition film, since the sedimentable components are sedimentedon a horizontal plane upon the electrodeposition coating. Thesedimentability can be evaluated from the Ra values of the horizontalappearance and the vertical appearance, as follows, if thesedimentability is acceptable or not acceptable.

Evaluation Basis for Sedimentability

Acceptable (O): Horizontal Ra value−Vertical Ra value=less than 0.05 μm

Not acceptable (X): Horizontal Ra value−Vertical Ra value=no less than0.05 μm

Measurement of Thermal Softening Temperature

The storage elasticity modulus G′ of a sample obtained by adjusting theconcentration of the crosslinked resin particles to 30% by weight (as asolid content) is measured from 90° C. under conditions of a strain of0.5 degree, a frequency of 0.02 Hz and a rising temperature rate of 4.0°C./min in a temperature dependent measurement with Rheosol-G3000(manufactured by UBM Corporation) that is a rotational type dynamicviscoelasticity measurement device. The measurement results are shown ina graph in FIG. 8. The tangential line in an area at which viscosity isa constant and the tangential line in an area at which the lowering ofviscosity occurs are drawn, and the temperature at the cross point isthe thermal softening temperature.

Evaluation Method for Edge Coatability

As described above, the edge coatability was evaluated. FIG. 9 is a viewschematically showing a point in a distance of 30 microns from the edgeof a cutter knife blade. If the thickness of the film on this point isno less than 7.8 μm, the edge coatability is acceptable.

The Measurement Method of Average Particle Size of Crosslinked ResinParticles

The average particle size of the crosslinked resin particles employed ineach of the above-described Examples and Comparative Examples wasmeasured according to the followings. The average particle size of thecrosslinked resin particles was measured by a granular particletransmission measurement method with MICROTRAC9340UPA manufactured byNikkiso Co., Ltd. Further, the particle size distribution of thecrosslinked resin particles was measured by the measurement device, andan average particle size at cumulative relative frequency F(x)=0.5 wascalculated from the measurement values. In these measurements andcalculations, the refractive index of a solvent (water) was 1.33, andthe refractive index of resin component was 1.59.

TABLE 2 Example 1B Example 2B Example 3B Example 4B Content of inorganicpigment (%) 0 0 3 0 Crosslinked resin Species Crosslinked resinCrosslinked resin Crosslinked resin Crosslinked resin particlesparticles #3 particles #4 particles #4 particles #4 Content (%) 15 15 1015 Degree of Middle Large Large Large crosslinking Thermal 120 140 140140 softening temperature Particle size (μm) 2.0 2.0 2.0 2.0Electroconductivity controlling agent — — — ◯ Melt viscosity  80° C./G″value 113 107 90 99 140° C./G′ value 125 475 222 188 Evaluation ofsedimentability ◯ ◯ ◯ ◯ Smoothness Ra (C/0 = 2.5) 0.21 0.23 0.23 0.22Edge coatability (μm) 7.8 8.0 7.9 7.8

TABLE 3 Comparative Comparative Comparative Comparative ComparativeExample 1B Example 2B Example 3B Example 4B Example 5B Content ofinorganic 23 0 0 0 0 pigment (%) Crosslinked Species — — CrosslinkedCrosslinked Crosslinked resin resin particles resin resin particlesparticles #1 particles #1 #2 Content (%) — — 5 10 15 Degree of — — LargeLarge Small crosslinking Thermal — — 140 140 107 softening temperatureParticle size — — 0.1 0.1 1.5 (μm) Electroconductivity — — — — —controlling agent Melt 80° C./G″ 89 23 156 228 94 viscosity value 140°C./G′ 155 21 73 110 75 value Evaluation of X ◯ ◯ ◯ ◯ sedimentabilitySmoothness Ra (C/0 = 2.5) 0.18 0.19 0.30 0.37 0.22 Edge coatability (μm)7.9 3.6 6.0 8.3 5.6

The degree of the crosslinking was described idepending on the thermalsoftening temperature and according to the measurement of the thermalsoftening temperature.

Degree of crosslinking (Large): Thermal softening temperature of 140° C.or more.Degree of crosslinking (Middle): Thermal softening temperature of 120°C. or more and less than 140° C.Degree of crosslinking (Small): Thermal softening temperature of 120° C.or lessCrosslinked resin particles #1: Crosslinked resin particles obtained inthe Production Example 5B.Crosslinked resin particles #2: CHEMISNOW SX-130M (under product name)manufactured by Soken Chemical & Engineering Co., Ltd.Crosslinked resin particles #3: GM-0105 (under product name)manufactured by GANZ Chemical Co., Ltd.Crosslinked resin particles #4: F-200 (under product name) manufacturedby Toyobo Co., Ltd.

As seen from the above Tables 2 and 3, it is understood that theelectrodeposition coating composition with a low ash content and a lowsolid content, which comprises the crosslinked resin particles having anaverage particle size within a range of from 1.0 to 3.0 μm and a thermalsoftening temperature within a range of from 120 to 180° C., couldprovide excellent performances superior in both of the smoothness andthe edge coatability. The performances are in a similar extent to thatof the Comparative Example 1B which is a conventional coatingcomposition. In the Comparative Example 1B, the electrodepositioncoating composition comprises a conventional inorganic pigment withoutany resin particles, which can provide a good surface smoothness and agood edge coatability. The electrodeposition coating composition has alow sedimentability evaluation degree, since the ash content therein ishigh. In the Comparative Example 2B, the electrodeposition coatingcomposition comprising no inorganic pigments and no resin particles canprovide a good smoothness and a highly deteriorated edge coatability.With respect to the Comparative Examples 3B to 5B, the electrodepositioncoating composition comprises resin particles. In the ComparativeExamples 3B and 4B, the particle size is small. In the ComparativeExample 5B, the thermal softening temperature is low. Therefore, theComparative Examples 3B to 5B would provide a poor edge coatability anda poor surface smoothness.

1. A cationic electrodeposition coating composition, which provides anuncured electrodeposited film having storage elasticity modulus (G′) at140° C. within a range of from 80 to 500 dyn/cm² and loss elasticitymodulus (G″) at 80° C. within a range of from 10 to 150 dyn/cm², andwhich is superior in smoothness and edge coatability.
 2. The cationicelectrodeposition coating composition according to claim 1, whichcomprises a cationic epoxy resin, a blocked isocyanate curing agent, andif necessary, a crosslinked resin particle and/or an inorganic pigment.3. A method for producing a cationic electrodeposition film havingestablished smoothness and edge coatability, wherein the cationicelectrodeposition film is prepared by applying a voltage to an articleimmersed in a cationic electrodeposition coating composition, whichincludes steps of: adjusting storage elasticity modulus of an uncuredelectrodeposited film of the cationic electrodeposition coatingcomposition (G′) at 140° C. within a range of from 80 to 500 dyn/cm²,and adjusting loss elasticity modulus of an uncured electrodepositedfilm of the cationic electrodeposition coating composition (G″) at 80°C. within a range of from 10 to 150 dyn/cm².
 4. The method according toclaim 3, wherein crosslinked resin particles having an average particlesize within a range of from 1.0 to 3.0 μm are added to the cationicelectrodeposition coating composition in order to adjust storageelasticity modulus and loss elasticity modulus.
 5. The method accordingto claim 4, wherein content of the crosslinked resin particles is 3 to15% by weight relative to weight of resin solid contents in the cationicelectrodeposition coating composition.
 6. The method according to claim3, wherein an inorganic pigment is added to the cationicelectrodeposition coating composition, wherein content of the inorganicpigment is 10 to 20% by weight relative to weight of solid contents inthe cationic electrodeposition coating composition, in order to adjuststorage elasticity modulus and loss elasticity modulus.
 7. The methodaccording to claim 3, wherein crosslinked resin particles having anaverage particle size within a range of from 1.0 to 3.0 μm and aninorganic pigment are added to the cationic electrodeposition coatingcomposition, wherein content of the inorganic pigment is 0.5 to 10% byweight relative to weight of solid contents in the cationicelectrodeposition coating composition, in order to adjust storageelasticity modulus and loss elasticity modulus.
 8. The method accordingto claim 7, wherein content of the crosslinked resin particles is 3 to15% by weight relative to weight of resin solid contents in the cationicelectrodeposition coating composition.